US3644806A - High-speed printer-paper feed engine - Google Patents

High-speed printer-paper feed engine Download PDF

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Publication number
US3644806A
US3644806A US22235A US3644806DA US3644806A US 3644806 A US3644806 A US 3644806A US 22235 A US22235 A US 22235A US 3644806D A US3644806D A US 3644806DA US 3644806 A US3644806 A US 3644806A
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Prior art keywords
velocity
responsive
tension
motor
current
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US22235A
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English (en)
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Ross A Belson
Gaston A Palombo
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Honeywell Inc
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Honeywell Inc
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K4/00—Generating pulses having essentially a finite slope or stepped portions
    • H03K4/02—Generating pulses having essentially a finite slope or stepped portions having stepped portions, e.g. staircase waveform
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
    • G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
    • G06K15/16—Means for paper feeding or form feeding

Definitions

  • a high-speed incremental web transport system especially suited for a high-speed printer application includes two motors with velocity feedback driven from a common controller in accordance with a computer originated movement request. Incremental position transducers allow precise repetitive spacing and positional stability of the motor shafts. Differential tension to be created during printing periods is obtained by controlling motor current. Synchronization control for skip-type movements prevents a buildup of positional error.
  • This invention relates to web transport systems. More specifically, the invention relates to a high speed paper transport system for use in printing out information from a computer. 1
  • the tractors which pull the paper under tension must overcome any contact friction between the paper and a guide surface contacting the paper. This puts additional tension upon the paper. Since tension above a certain critical value will tear the paper, the tension needed to hold the paper taut during printing, plus the necessary acceleration tension must remain below this critical tearing value. Therefore, the tension to hold the paper taut during printing may have to be lower than actually desired.
  • the tension can only be adjusted initially and varies with the mechanical inaccuracies introduced by the various system linkages.
  • the present invention provides an improved positioning control system through the use of two separate motor means with velocity feedback to each motor means to control the two web carrying tractors.
  • the two motor means are driven from a common velocity function generator which, in response to a given computer movement request, generates a velocity waveform to accomplish the desired movement.
  • each motor means is also coupled to a position transducer which is selectively connected in a feedback configuration for precise'and positive stop position placement of the rotating portion of each motor means.
  • means responsive to the torque generated by the motor means when the web is not moving adds a signal to at least one of the motor means to provide tension of any desired quantity.
  • each motor means includes a motor and a drive amplifier.
  • each rotating portion includes a shaft.
  • the invention may be embodied as a basic velocity servosystem with three auxiliary control loops activated under predetermined conditions.
  • the basic system includes two amplifiers for driving the two motors, with two paper carrying tractors and a tachometer coupled to each motor. Both amplifiers, in addition to their respective tachometer signal, also receive a common command from a velocity function generatOI.
  • the velocity function generator upon receipt of a paper movement request from a computer, provides a velocity waveform which each amplifier and motor combination can closely follow.
  • the polarity of the velocity waveform causes the motors to run in either a forward or reverse direction.
  • the position transducers are each of the multiple null type to produce a null at each possible desired stopping location for the motor shaft and tractors that move the paper.
  • Switch means apply the position signals to the motor means when the final position is reached.
  • the switch means maintains the application of the position signals until the next desired paper movement request is received by the velocity function generator and acted upon.
  • the torque responsive means measures the current provided by the amplifiers to each motor and a tension control signal is provided to one of the motor-amplifier combinations to keep a constant current difference between the two motors. Since current is proportional to the torque provided by the motor, a given current difference between the two motors means that a constant tension is provided to the paper web carried between the tractors.
  • FIG. 1 is an elevation showing two motors coupled to webcarrying tractors with a tachometer and a position transducer also coupled to each motor shaft.
  • FIG. 2 is a block diagram showing a system embodying features of the invention.
  • FIG. 3 is a block diagram detailing the velocity function generator in FIG. 2.
  • FIG. 4 is an electrical schematic of the ramp generator of FIG. 2.
  • FIG. 5 shows some typical velocity waveforms from the velocity function generator in FIG. 2.
  • FIG. 1 two electric motors, 1 and 3 drive respective shafts 5 and 7 on which are mounted web carrying tractors 9, 11, I3, and 15. These tractors have radially extending projections 17 which engage with holes 18 in a paper web 19.
  • the paper web 19 is usually horizontally perforated into pages 20 of a length sufi'icient to accommodate about ninety print lines.
  • the first printed line of a page is known as the head-of-form.
  • Two tachometers 25 and 27 are connected to the motor shafts 5 and 7 and provide an output indicative of motor, and hence paper-carrying tractor, velocity.
  • a computer 31 which furnishes the information to be printed ori ginates a request for a desired paper movement.
  • the request is communicated in a digital form over lines 33 to velocity function generator 35.
  • the velocity function generator 35 examines the direction and amount of movement requested and generates an appropriate velocity waveform on line 37 for accomplishing this movement in an optimal manner.
  • the velocity waveform moves between predetermined velocity levels along carefully controlled inclined ramps (see FIG. 5). The slope of the ramp is chosen in order that the motors 1 and 3 with their associated amplifiers 39 and 41 respectively will be able to continuously achieve velocities essentially equal to that commanded by the velocity waveform.
  • Line 37 is connected to amplifiers 39 and 41 through respective summing junctions 43 and 45 which serve to sum together various signals such as the velocity feedback signals provided by tachometers 25 and 27 and the velocity waveform on line 37.
  • the position transducers 21 and 23 are coupled to the motors 1 and 3 respectively and their output signals are connected through switches 47 and 49 to the summing junctions 43 and 45 respectively.
  • the switches 47 and 49 respond to a decrement or line counter in the velocity function generator 35 to remain open during signals which induce normal motion.
  • the switches 47 and 49 simultaneously close in response to signals from the counter in the velocity function generator. Closing of the switches creates a position loop for precisely holding the tractor at a desired final location.
  • the switches 47 and 49 are simultaneously opened at the start of a paper movement during a signal from the function generator 35 that again induces motion.
  • the switches 47 and 48 may for example comprise FET transistors connected with their respective paths of major current flow (i.e., source to drain) between transducer 21 and summing junction 43 and between trans ducer 23 and summing junction 45 respectively.
  • the velocity function generator 35 controls the control electrodes.
  • Position transducer 21 is also connnected to the velocity function generator 35 by a line 50 and serves to provide an indication of distance moved.
  • the velocity function generator 35 responds by providing appropriate lower levels of commanded velocity as the motors 1 and 3 approach the final desired position.
  • the signal on line 50 is processed by the velocity function generator 35 to provide an internal signal indicative of a null being traversed. This internal signal is used to decrement the internal line counter (see FIG. 3).
  • the essentially sinusoidal cyclical'signals from position transducers 21 and 23 are fed into squaring amplifiers 51 and 52 respectively.
  • the squaring amplifiers 51 and 52 amplify and clip the sinusoidal input so as to produce a square wave output in phase with the sinusoidal input.
  • the outputs of squaring amplifiers 51 and 52 are passed to a phase comparator 53 which provides an output indicative of the phase difference between the leading edges of the squaring amplifier outputs.
  • phase comparator 53 passes to either line 55 or 57 depending upon which squaring amplifier output edge is leading.
  • the signals on lines 55 and 57 are each applied to both summing junctions 43 and 45 with opposite polarities.
  • the squaring amplifiers may be composed of amplifiers followed by clipping circuits. They may then have further amplification of the clipped signal.
  • phase comparator 53 produces an output on line 57 proportional to the indicated phase difference between position transducers 21 and 23.
  • This signal on line 57 provides an additional signal to summing junction 45 to augment the velocity waveform signal on line 37.
  • the signal at summing junction 43 is treated as a negative signal and thus subtracts from the velocity waveform provided by line 37 This causes motor 1 to slow down and motor 3 to speed up such that the outputs of position transducers 21 and 23 are brought into synchronism.
  • the tachometers 25 and 27 are accurate enough such that the positional difference buildup between the two motors 1 and 3 for a short, low-speed paper movement does not require correction.
  • Two motor-current-measuring resistors 63 and 65 are connected to a summing junction 67 which provides the difference therebetween to an amplifier 69 whose output is compared with a preset manually adjustable tension reference voltage source 71 by a summing junction 73 and the difference therebetween provided to tension control amplifier 75 whose output is connected to summing junction 43 through switch 77.
  • Switch 77 may also be composed of an FET transistor corresponding to switches 47 and 49. Switch 77 closes and opens in coincidence with switch 47 such that tension is only supplied when the two motors 1 and 3 are stopped. Switches 47, 49, and 77 are all controlled by line 79 from the line counter in the velocity function generator 35. Thus, tension is released before paper movement commences.
  • This tension control loop operates to keep a fixed difference in current through the two motors 1 and 3 when they are stopped. This assures constant tension throughout the printing operation.
  • FIG. 3 is a block diagram of the internal structure of the velocity function generator 35.
  • Computer 31 produces a digital request signal on lines 33 indicative of the number of print lines the paper 19 is to move. These signals are received by request logic unit 81 which interprets the request signal from computer 31 and produces a number representative of the print lines to be traversed. This number is stored in line counter 83 which makes this number available to a level generator 87 over lines 85. A nonzero number in the line counter 83 produces a signal on line 79 to open switches 47, 49, and 77. When the number is zero, the signal on line 79 will close the switches.
  • Level generator 87 is responsive to the digital number on lines 85 to produce discrete voltage levels on line 89 dependent upon the range of the number indicated by lines 85.
  • the level generator 87 when the number in line counter 83 is one or two, the level generator 87 produces a voltage on line 89 sufficient to drive the motor-amplifier combination at a low velocity of about 25-30 inches per second. If the number in line counter 83 is typically between three and seven, then level generator 87 produces a voltage on line 89 sufficient to drive the motor-amplifier combination .at a velocity of about 70 inches per second. If the number in line counter 83 is above seven, then level generator 87 produces a voltage sufficient to cause a velocity of about inches per second.
  • ramp generator 91 has an input of discrete voltage levels which are dependent upon the number in line counter 83. In response to the discrete levels on line 89, ramp generator 91 produces an output on line 37 in which the abrupt level changes on line 89 are connected by ramps of controlled slope. The signal on line 37 is that actually supplied to summing junctions 43 and 45.
  • Position transducer 21 is connected by line 50 to a null detector 82.
  • Null detector 82 is responsive to the null crossings of the position transducer output so as to generate a signal capable of decrementing line counter 83.
  • line counter 83 maintains the current count of print lines yet to be traversed.
  • FIG 4 is an electrical schematic diagram of the ramp generator 91. Equal and opposite supply voltages are supplied at terminals 101 and 103. Zener diodes 105 and 107 in conjunction with resistors 109 and 111 serve to establish substantially constant voltages at the points between the resistors 109 and 111 and the diodes 1 l7 and 133 respectively.
  • Lead 123 connects the collectors of transistors 121 and 131, the series combination of capacitor 135 and resistor 137, and the input of a buffer amplifier 139.
  • the buffer amplifier 139 prevents leakage of charge stored in the capacitor and the amplifier output is the velocity waveform on line 37.
  • zener diode 117 acts in conjunction with resistor 119 and transistor 121 to establish a constant current through resistor 119 and into lead 123.
  • Diode 125 provides temperature compensation for the base emitter junction of transistor 121.
  • zener diode 127 acts in conjunction with resistor 129 and transistor 131 to require a constant current from lead 123.
  • Diode 133 serves to temperature compensate for the base emitter junction of transistor 131.
  • the current set by zener diode 117 to flow through transistor 121 into lead 123 is essentially equal to that set by zener diode 127 to flow from lead 123 through transistor 131.
  • transistors 121 and 131 cooperate to pass a preset level of current between the positive and negative voltage supplies. Therefore, no current is supplied to or drawn from capacitor 135 and the voltage on lead 123 remains constant.
  • Line 37 is connected to input terminal 141 of high-gain amplifier 113.
  • output line 115 will be at its quiescent level. Such a condition is indicative of the fact that the voltage on line 37 is equal to the discrete voltage levels provided on line 89 by level generator 87.
  • level generator 87 changes the zero voltage level on line 89 to a nonzero level. Therefore, high-gain amplifier 113 causes output line 115 to assume a level other than the quiescent level. For example, if the voltage on line 89 goes from zero volts to some positive voltage value, then the signal on line 115 goes negative. This negative voltage is sufficient to cutoff, transistor 131. Zener diodes 105 and 107 establish voltages that allow the maximum voltage swings on line 115 to positively cutoff transistors 121 and 131. However, transistor 121 will not be affected and will continue to act as a current source. Since the current through transistor 12] into lead 123 can no longer fiow through transistor 131 and resistor 129 to the negative source, it must flow into the series combination of capacitor 135 and resistor 137.
  • Resistor 137 in series with capacitor 135 acts to put a small voltage step at the start of the ramp on line 37 by virtue of the current through the resistor. There is no corresponding voltage step at the end of a ramp because of the voltage feedback to amplifier terminal 141. This improves operation of the servo system by providing an increased signal at the beginning of a velocity change operation which serves to overcome the natural lag associated with the transport servo system.
  • FIG. 5 shows some typical velocity wavefonns produced on line 37 for various desired movement distances.
  • Curve 151 shows the velocity waveform generated for a movement of one print line.
  • Waveform 153 shows the velocity waveform generated for a movement of six print lines.
  • Waveform 155 shows the velocity waveform produced for a movement of 16 print lines.
  • Position transducer 23 is located at a null by virtue function of the feedback connection and position transducer 21 is slightly offset from null because of the tension control signal provided by amplifier 75.
  • This tension signal is such as to maintain a fixed difference, determined by the preset tension reference voltage 71, between the currents in resistors 63 and Now if computer 31 issues a request over lines 33 to velocity function generator 35 for a desired number of print lines to be traversed, the following steps will occur. After receipt of the request by the request logic unit 81, the computer request is interpreted and the number of lines to be traversed is placed in line counter 83.
  • line counter 83 will be decremented and eventually cause level generator 87 to produce a lower voltage level on line 89.
  • Ramp generator 91 will then cause line 37 to linearly approach this new commanded voltage level.
  • Motors 1 and 3 continually closely follow the velocity waveform on line 37. For a requested movement of 16 print lines in the forward direction, the motor velocity would substantially have the shape of waveform in FIG. 5.
  • the summing junctions are composed of known types of adding circuits which where necessary include inversion inputs or outputs so that inputs may be added or subtracted as described.
  • the synchronizing loop including elements 21, 23, 51, 52, 53, 43, and 45, allows the maintenance of equal velocity for the two tractors despite the inaccuracies of the tachometers and high motor speeds. It does this by comparing the position transducer signals and generating a velocity correction signal for the motor means in response to the compared signals.
  • a web transport system comprising:
  • velocity function generator means for providing a velocity waveform to both of said closed loop velocity feedback means
  • control means connected to said velocity function generator means for varying the velocity waveform.
  • control means includes a position-indicating means responsive to a first one of said motor means to provide an output indicative of the position of said rotating portion.
  • An apparatus as in claim 2 further comprising second position-indicating means responsive to a second one of said motor means to provide an output indicative of the position of said rotating portion;
  • each of said position feedback means includes switch means responsive to said velocity function generator means for selectively connecting and disconnecting said position feedback means during predetermined portions of the velocity waveform.
  • the apparatus of claim 1 additionally comprising tensionmeasuring means for measuring tension applied by the motor means to the web;
  • control loop means responsive to said tension measuring means and to said velocity function generator means for providing a signal to one of said motor means during predetermined portions of the velocity waveform.
  • tensionmeasuring means includes current measuring means for producing signals in response to current in said motor means.
  • said tension-measuring means comprises current-measuring means responsive to the current in each of said motor means to provide an output indicative of the difference therebetween;
  • tension control amplifier means in said control loop means responsive to said current-measuring means and a predetermined value of current to provide an output indicative of the difference therebetween;
  • tension control switch means in said control loop means responsive to predetermined portions of the velocity waveform for connecting said tension control amplifier means to one of said motor means.
  • the apparatus ofclaim 3 additionally comprising synchronization loop means including position differencemeasuring means responsive to said position-indicating means for providing an indication of the difference therebetween to one of said motor means.
  • a servosystem comprising a pair of motor means having respective shafts;
  • velocity function generator means for responding to a request signal and providing a velocity waveform to both said motor means
  • two position-indicating means each responsive to a respective one of said motor means to provide an output indicative of the respective positions of said shafts
  • two position feedback means each connecting one of said position-indicating means to a respective one of said motor means and including switch means responsive to said velocity function generator means for selectively connecting and disconnecting said position feedback means during predetermined portions of the velocity waveform
  • control means responsive to one of said position-indicating means and connected to said velocity function generator rn means for varying the velocity waveform
  • synchronization loop means comprising position difference measuring means responsive to said position indicating means for providing an indication of the difference therebetween to one of said motor means.
  • control loop means responsive to said tension-measuring means and to said velocity function generator means for providing a signal to one of said motor means during predetermined portions of the velocity waveform.
  • said tension-measuring means includes current-measuring means responsive to the current in each of said motor means to provide an output indicative of the difference therebetween;
  • tension control amplifier means in said control loop means responsive to said current-measuring means and a predetermined valve of current to provide an output indicative of the difference therebetween;
  • tension control switch means in said control loop means responsive to predetermined portions of the velocity waveform for connecting said tension control amplified means to one of said motor means.
  • a high-speed computer line printer comprising a velocity function generator responsive to a computer request signal for generating a velocity waveform
  • two velocity-indicating means adapted to provide respective tractor velocity indicating signals to said respective amplifier inputs;
  • two position transducers each coupled to one of said motors, having cyclical outputs with a null crossing for each possible desired stopping position of said tractors;
  • generator means includes a ramp generator for producing a and linear change in output in response to discrete changes in tellsion cont")! means pf to f P ll tension input comprising two equal current sources connected in selng measurement to provide a tension signal to one of said fies;

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Handling Of Sheets (AREA)
  • Control Of Multiple Motors (AREA)
  • Control Of Electric Motors In General (AREA)
  • Handling Of Continuous Sheets Of Paper (AREA)
  • Control Of Stepping Motors (AREA)
  • Character Spaces And Line Spaces In Printers (AREA)
  • Controlling Rewinding, Feeding, Winding, Or Abnormalities Of Webs (AREA)
US22235A 1970-03-24 1970-03-24 High-speed printer-paper feed engine Expired - Lifetime US3644806A (en)

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US2223570A 1970-03-24 1970-03-24

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US3644806A true US3644806A (en) 1972-02-22

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US (1) US3644806A (en:Method)
JP (1) JPS5526506B1 (en:Method)
CA (1) CA940214A (en:Method)
DE (1) DE2114331C3 (en:Method)
FR (1) FR2085036A5 (en:Method)
GB (2) GB1356014A (en:Method)
NL (1) NL7103938A (en:Method)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3733529A (en) * 1972-05-22 1973-05-15 Ross Controls Corp Plural motor tape drive speed control
US3969663A (en) * 1974-10-17 1976-07-13 Storage Technology Corporation Capstan control for a tape drive system
US4051415A (en) * 1975-03-05 1977-09-27 Braemar Computer Devices, Inc. Web speed control system
US4095146A (en) * 1976-05-10 1978-06-13 Raymond Engineering Inc. Reel-to-reel drive with speed control
US4174237A (en) * 1978-07-03 1979-11-13 International Paper Company Process and apparatus for controlling the speed of web forming equipment
US4431950A (en) * 1982-07-28 1984-02-14 Cetec Corporation Capstan drive system for high speed tape duplicator
US4538516A (en) * 1979-04-16 1985-09-03 Somerset Technologies, Inc. Torque-assist system for printing belts
GB2203863A (en) * 1987-04-21 1988-10-26 El Gammal Hussein Mokhtar Phase control for master-slave system
US4802777A (en) * 1981-10-19 1989-02-07 Canon Kabushiki Kaisha Print wheel and carriage drive system for a printer
US6326747B1 (en) * 1998-12-21 2001-12-04 Kabushiki Kaisya Tokyo Kikai Seisakusho Method and device for synchronization control
US20040215582A1 (en) * 2000-12-08 2004-10-28 Pitney Bowes Incorporated Synchronization method and apparatus in a value metering system having a digital print head
US20060267529A1 (en) * 2005-05-31 2006-11-30 Piefer Richard W Position feedback device with prediction
US20070003305A1 (en) * 2005-07-01 2007-01-04 Xerox Corporation Current measurement circuit for transformer with high frequency output
US20080218576A1 (en) * 2007-03-07 2008-09-11 Xerox Corporation Escort belt for improved printing of a media web in an ink printing machine

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT1159280B (it) * 1982-05-18 1987-02-25 Necchi Spa Unita' automatica per eseguire ricami
GB8331899D0 (en) * 1983-11-30 1984-01-04 Markem Syst Ltd Label printing machines
CN112074545B (zh) 2018-04-26 2022-04-22 大金工业株式会社 精制含氟聚合物的制造方法

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3733529A (en) * 1972-05-22 1973-05-15 Ross Controls Corp Plural motor tape drive speed control
US3969663A (en) * 1974-10-17 1976-07-13 Storage Technology Corporation Capstan control for a tape drive system
US4051415A (en) * 1975-03-05 1977-09-27 Braemar Computer Devices, Inc. Web speed control system
US4095146A (en) * 1976-05-10 1978-06-13 Raymond Engineering Inc. Reel-to-reel drive with speed control
US4174237A (en) * 1978-07-03 1979-11-13 International Paper Company Process and apparatus for controlling the speed of web forming equipment
US4538516A (en) * 1979-04-16 1985-09-03 Somerset Technologies, Inc. Torque-assist system for printing belts
US4802777A (en) * 1981-10-19 1989-02-07 Canon Kabushiki Kaisha Print wheel and carriage drive system for a printer
US4431950A (en) * 1982-07-28 1984-02-14 Cetec Corporation Capstan drive system for high speed tape duplicator
GB2203863A (en) * 1987-04-21 1988-10-26 El Gammal Hussein Mokhtar Phase control for master-slave system
USRE40165E1 (en) * 1998-12-21 2008-03-25 Kabushiki Kaisya Tokyo Kikai Seisakusho Method and device for synchronization control
US6326747B1 (en) * 1998-12-21 2001-12-04 Kabushiki Kaisya Tokyo Kikai Seisakusho Method and device for synchronization control
US20040215582A1 (en) * 2000-12-08 2004-10-28 Pitney Bowes Incorporated Synchronization method and apparatus in a value metering system having a digital print head
US7213987B2 (en) * 2000-12-08 2007-05-08 Pitney Bowes Inc. Synchronization method and apparatus in a value metering system having a digital print head
US20060267529A1 (en) * 2005-05-31 2006-11-30 Piefer Richard W Position feedback device with prediction
US7456599B2 (en) * 2005-05-31 2008-11-25 Rockwell Automation Technologies, Inc. Position feedback device with prediction
US20070003305A1 (en) * 2005-07-01 2007-01-04 Xerox Corporation Current measurement circuit for transformer with high frequency output
US7197268B2 (en) * 2005-07-01 2007-03-27 Xerox Corporation Current measurement circuit for transformer with high frequency output
US20070170932A1 (en) * 2005-07-01 2007-07-26 Xerox Corporation Power supply with current measurement circuit for transformer with high frequency output
US7411406B2 (en) 2005-07-01 2008-08-12 Xerox Corporation Power supply with current measurement circuit for transformer with high frequency output
US20080218576A1 (en) * 2007-03-07 2008-09-11 Xerox Corporation Escort belt for improved printing of a media web in an ink printing machine
US8025390B2 (en) 2007-03-07 2011-09-27 Xerox Corporation Escort belt for improved printing of a media web in an ink printing machine

Also Published As

Publication number Publication date
DE2114331B2 (de) 1978-11-16
JPS5526506B1 (en:Method) 1980-07-14
FR2085036A5 (en:Method) 1971-12-17
NL7103938A (en:Method) 1971-09-28
DE2114331A1 (de) 1971-10-14
DE2114331C3 (de) 1979-07-26
GB1356015A (en) 1974-06-12
CA940214A (en) 1974-01-15
GB1356014A (en) 1974-06-12

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