US 3656041 A
Apparatus for controlling the paper feeding in printing apparatus, wherein the feed motor speed is controlled by the combined effect of a speed-space detector whose output is speed-proportional voltage and said pulses are compared with a predetermined pulse number, and wherein the results of said comparison are employed in combination to provide a suitable paper feed power control through a bidirectional amplifier which does not require a stabilized power supply.
Description (OCR text may contain errors)
United StatesPatent' Bonzano  APPARATUS FOR CONTROLLING TIE FEEDING OF PAPER IN HIGH-SPEED PRINTERS  Inventor:
Giorgio Bonzano, Caluso, Italy Honeywell Information Systems Italia S.p.A., Turin, Italy Filed: July 14, 1970 Appl. No.: 54,815
Foreign Application Priority Data I July 17, 1969 Italy ..19733 A/69 Assignee:
US. Cl ..3l8/318, 197/133, 226/43, 330/30 Int. Cl. ..G05b 5/00, H02p 5/00, B41j 15/00 Field ofSearch ..318/314, 318, 329, 326, 604, 318/605; 197/133; 226/2, 43, 45 References Cited UNITED STATES PATENTS 2,927,258 3/1960 Lippel 3....318/604 x LOGIC DEVICE 5 l REFERENCE VOLTAGE l /GENERATOR VOLTAGE 17 C OMPARATOR H AMPLIFIER  3,656,041 [451 Apr. 11, 1972 3,452,258 6/1969 Thompson ..318/604 3,504,362 3/ 1970 Feldmann ..3 18/604 X 3,452,853 7/1969 Mabon ..226/43 X 3,323,700 6/1967 Epstein et al. ..226/45 X Primary Examiner-J. D.v Miller Assistant Examiner-Robert J. Hickey Attorney-George V. Eltgroth, Lewis P. Elbinger, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman  ABSTRACT Apparatus for controlling the paper feeding in printing apparatus, wherein the feed motor speed is controlled by the combined effect of a speed-space detector whose output is speed-proportional voltage and said pulses are compared with a predetermined pulse number, and wherein the results of said comparison are employed in combination to provide a suitable paper feed power control through a bidirectional amplifier which does not require a stabilized power supply.
4 Claims, 6 Drawing Figures maooqqo Patented April 11, 1972 3,656,041
5 Sheets-Sheet 1 DEVICE a s 9 REFERENCE VOLTAGE GENERATOR r VOLTAGE COMPARATOR.
AM PL|F|ER 1 r s Giorgi o BONZA N0 INVEN'I'OR.
Patented A ril 11, 1912 3,656,041
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I ployed in information BACKGROUND OF INVENTION This invention relates to apparatus for controlling the paper feeding in high-speed printers, particularly in printers emprocessing systems. Accordingly, this invention concerns apparatus for controlling the acceleration, the braking, and the reversal of a low inertia motor according to a'predetermined sequence.
The feeding of paper in high-speed printers is usually provided by means of a motor which drives a system of sprocket,
or toothed, wheels or chains, whose teeth engage in a set of sprocket holes provided in the paper. The distance of the paper advancement must be an integral multiple of a definite quantity, usually the minimum spacing between consecutive printed lines. This quantity is called the line pitch.
According to requirements, the paper may be controlled to advance, in response to an appropriate line feed signal, one,
, two, or even three line pitches at a time during normal printing operations, to obtain printed texts of different densities. The paper may also be controlled to advance through a large number of line pitches by the slew operation, in which a substantially large portion of blank space is interposed v between portions of printed text.
Apparatus is known for precisely controlling the position of the paper at the end of each line feed or slew operation. This usually comprises mechanical means, such pin-and-ratchet devices, gears, and the like. However, devices are costly and are subject to considerable wear and tear as a consequence of the mechanical stresses to which they are subjected. Moreover, they are usually noisy and frequently go out of adjustment.
Other feed control apparatus uses low inertia motors for directly controlling the paper feed operation. Such motors may be, for example, direct current motors with printed-circuit rotors, controlled by bidirectional amplifiers suitable for v imparting to the motor high accelerating or decelerating torques. The paper feed operation requires, in this instance,
three states: a first state of fast acceleration, a second state of I constant speed and a third state of fast deceleration (braking). In the first state the controlling amplifier delivers a large current of predetermined polarity, in the second state the current delivered is only that required to compensate for the energy lost by friction in order to maintain the motor at constant speed, and in the third state the amplifier delivers a large current of reversed polarity. To obtain the same distance of line pitch in each state, the motor speed and, therefore, the amplifier current delivered in each state, must be precisely controlled, so that, under like control conditions, the paper advances the same number of line pitches during equal intervals.
It is therefore necessary for the motor control amplifier to have an output almost perfectly stable and independent of external conditions. In particular, in the prior art, great im portance is given to stabilizing the direct current source delivering the current controlled by the motor control amplifier. However, precise stabilization of a large d-c current source is very burdensome and costly.
Therefore, it is the object of the instant invention to provide a paper feed control system of low cost, great accuracy and high reliability.
SUMMARY OF THE INVENTION According to the invention this object is attained by supplying the motor from a bidirectional amplifier which is controlled by a signal provided from comparing a reference voltage and a voltage generated by a tachometric generator driven by the motor. Stabilization of the current delivered by the amplifier is obtained in a simple and efficient manner by stabilizing an intermediate stage of the amplifier utilizing low power Zener diodes.
Although the invention is primarily directed toward paper feeding in a high-speed printer, it may be used in a number of 2 other instances wherein it is necessary to control acceleration, constant speed, and deceleration and reversal a rotating mechanical device driven by a low-inertia motor. For example, the invention is useful with the tape transport capstan of a tape handler of the single capstan type.
BRIEF DESCRIPTION OF THE DRAWING The invention will be described with reference to the accompanying drawings, wherein:
FIG. 1 is a block diagram, including a perspective view of a portion of a high-speed printer of the invention;
FIG. 2 illustrates waveforms of various voltages and currents in the embodiment of FIG. 1;
FIG. 3 is a schematic diagram of the reference voltage generator and voltage comparator of the invention;
FIG. 3a is a diagram of the equivalent circuit of the voltage comparator of FIG. 3;
FIG. 4 is a schematic diagram of the bidirectional amplifier of F IG. 1; and
FIG. 5 is a schematic diagram of a variation of the amplifier of FIG. 4;
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a paper feed motor 1 drives a toothed chain member 2. Member 2 engages sprocket holes in and thereby moves a paper web 3. Either shaft of motor 1, or on another shaft directly driven by the motor, are mounted a photodisc 4, and a tachometric d-c generator 7. Disc 4 is provided at its periphery with a set of uniformly spaced holes associated with a photoelectric pick-up device which comprises a lamp 5 and a photocell, or photodiode, 6. Generator 7 delivers at its terminals a voltage proportional to the rotational speed of motor 1.
The distance between adjacent holes on the periphery of photodisc 4 corresponds to the angle through which motor 1 must rotate to advance paper web 3 by a single line pitch. receives a light pulse, and delivers an electric pulse, each time that the paper web advances a line pitch.
The paper feeding occurs either step-by-step," each step spanning one, two or three line pitches, or by slewing," wherein the paper web advances through a substantially larger number of line pitches. Although slewing may occur at different speeds, depending on amount of spacing required, the slew speed is always greater than the step-by-step speed. For example, three speeds may be employed: a low speed for the step-by-step advancement, an intermediate speed for slow slewing, and a high speed one for fast" slewing. Possible values for these three speeds may be 600 mm/sec., 1,000 mm/sec., and 1,800 mm/sec.
In FIG. 1, a logical device 8 receives, instruction signals on an input lead 9. The instruction signals correspond to the required type of feeding; i.e., step-by-step feeding by one, two or three line pitches, slow slew or fast slew, and number of pitches per slew operation. The pulses delivered by photocell 6 are supplied to logical device 8 on an input lead 10.
Logical device 8 responds to the instruction signals to control a reference voltage generator 11, which generates a reference voltage V for determining the rotational speed of motor 1. The reference voltage generated by generator 11 is applied to an input lead 12 of a comparator 13. Comparator 13 compares two voltages, reference voltage V and a voltage V termed the tachometric voltage. The tachometric voltage V which is proportional to the voltage generated by tachometric generator 7, is applied to input lead 14. The ratio between the tachometric voltage V and the voltage delivered by generator 7 is so chosen, that for each different reference voltage, the tachometric voltage provided at the corresponding motor speed is slightly lower than voltage V Assume, first, that this ratio is equal to unity, wherein voltage V is the same as the actual voltage delivered by generator 7. In comparator 13, the tachometric voltage is subtracted from the reference voltage. The difference voltage delivered by comparator 13 is aicontrol voltage V which is applied to an input lead 15 of a bidirectional amplifier 16. This difference voltage may be positive, if the reference voltage is higher than the tachometric voltage, in which case the output lead 17 of amplifier l6 delivers a positive control current which causes motor 1 to rotate in a direction appropriate for feeding the paper. If the difference voltage is negative, amplifier 16 supplied to the motor a negative control current, which has a braking effect. If the difference is zero, the motor is not supplied with control current.
The waveforms of FIG. 2 illustrate the reciprocal relationship between the tachometric voltage V and the control volt-,
age V and illustrate the current delivered to the motor, for the example of a fast slewing. In this example, responding to the received instruction signals, logical device 8 selects a reference voltage representing the fast slew. Line R (waveform a) represents this reference voltage V and line T represents the corresponding tachometric voltage V Initially, when motor 1 is at rest, the tachometric voltage is zero, so that the control voltage V which is the difference between voltages V and V and is represented by line S (waveform b), is equal to reference voltage V Accordingly, amplifier 16 delivers a positive control current I as shown by line I (waveformr') 7 mg, I a, W 4 mm As the motor starts turning and increases its speed, the tachometric generator delivers an increasing voltage as represented by line T. The control voltage V correspondingly decreases, as shown by line S, which is the difference between the ordinates of lines R and T. When voltage V becomes less than a predetermined threshold value W, corresponding to the saturation conditions of amplifier 16, the control current out-- put I decreases from its initial maximum value I and, therefore, the acceleration and the slope of curve T decrease. When the control current is only sufficient to compensate for frictional losses, the acceleration becomes zero and the motor runs at constant speed.
During the rotation of motor 1, the pick-up device associated with photodisc 4 transmits a number of pulses, equal to the number of line pitches advanced, to logical device 8. Logical device 8 counts these pulses by means of a counter. When the number of pulses received by device 8 reaches a quantity n-k, wherein n is the programmed number of line pitches of the current slew, and k is an integer suitably chosen, for example 5, reference voltage V is reduced to the value V corresponding to step-by-step feeding. Accordingly, V becomes lower than V and a negative control voltage V is delivered to amplifier 16, which thereupon delivers a negative control current I,,, This negative control current abruptly slows motor 1 and reduces its speed to the step-by-step value.
This braking action requires the duration of k photodisc pulses. When the n pulse is received by logical device 8 the reference voltage is reduced to zero, the control voltage V again goes negative, and the braking current brings the motor to a halt.
It is apparent that the precision of the final position reached by the paper web at the end of a feeding operation is conditioned by the precision of action controlled by the braking current. If such action is too strong, the paper web halts too early, whereas if it is too weak, the paper overshoots the intended final position.
Reference voltage generator 11, FIG. 3, comprises three transistors T T and T for example of the NPN type. The collectors of these transistors are supplied from a common positive voltage source, +V, (for example, +20 v) through respective resistors R R R The emitters of transistors T T and T are grounded. The collectors of transistors T T .and T are also connected to the anodes of the respective diodes D,,'D and D The cathodes of these three diodes are all connected to one end 25 of a potentiometer R whose other end is grounded. The bases of transistors T,, T and T are connected to the respective input terminals 21, 22, 23.
device 8, which correspond to the required reference voltage to be delivered. The control signals on terminals 21, 22, and 23 represent binary values, the binary 1 being represented by a positive voltage (for example instance +5 V), and the'binary 0 being represented by 0 v.
When a binary 1 signal; i.e., a positive voltage, is applied to all of the three input terminals 21, 22, 23, the three transistors T,, T and T conduct, their collector voltages drop practically to 0 v and, consequently, point 25 drops to 0 v. Accordingly, reference voltage V on lead 12 is at 0 v. In this instance, motor 1 is supplied with no current and no paper feeding occurs.
If a binary 0 signal is applied to input terminal 21, while input terminals 22 and 23 receive binary l signals, transistor T becomes non-conductive. Current flows through resistor R,, diode D and potentiometer R Accordingly, lead 12 is brought to a reference voltage V which depends on the values of resistor R and potentiometer R and the position of the movable tap of potentiometer R Since the resistance of resistor R is considerably greater than that of potentiometer R the reference voltage V is substantially less than the source voltage, +V,. By adjusting the movable tap of potentiometer R the value of voltage V is brought to that required for stepby-step feeding.
If a binary 0 signal is applied to both input terminals 21 and 22, transistors T and T become non-conductive. Resistors R and R effectively become parallel connected through respective diodes D and D The resulting resistance value is lower than in the immediately preceding case, so that the reference voltage at lead 12 is higher, being a reference voltage V required for the slow slew.
If a binary 0 is applied to both input terminals 21 and 23, resistors R and R become effectively parallel connected. Since the value of resistor R is relatively small with respect to that of resistor R the resulting resistance value is further reduced. Therefore the voltage at lead 12 is relatively high, being the reference voltage V required for the fast slew.
The following table gives the binary values applied to the input terminals for each of the four control conditions, and the related reference voltages provided:
Condition Input Terminals Ref. Voltage No feeding l l l O Step-by-step 0 l l V Slow slew 0 0 l V,
Fast slew 0 l 0 V,-
Only four of the eight possible combinations of binary values at the three input terminals are used herein. Therefore, four remaining combinations are available if additional reference voltages are needed. The choice of the four combinations is only representative; different combinations may be selected depending on the resistance values and disposition employed. Moreover, since only four reference voltages are employed in the preferred embodiment, only two input terminals are required to provide the four different combinations of applied binary values. However, such an arrangement might set too rigid a constraint on the voltage values obtainable from particular resistance values. Instead, with the disclosed arrangement the values of the three resistances may be freely chosen to obtain the most suitable ratio between the three required feeding speeds.
The movable tap of potentiometer R permits adjusting the step-by-step feeding speed to the required value. If R represents the portion of potentiometer R between the movable tap and ground, the reference voltage V is proportional to R. However, the ratios between the various reference voltages are independent of R, depending only on R,, R R and R Thus, adjusting the potentiometer tap does not change the ratios between the speeds.
A set of suitable values for these resistances is, for example, the following:
responding speeds are:
R R 2.2 Kohm R 400 ohm R,,= 500 ohm which provide the following set of reference voltages:
where V is the value of the voltage source.
Thus, the ratios between reference voltages and cor- If the step-by-step feeding speed is, for example, 22 inches per second (560 mm/s) the slow slew speed is appr. 37 /?inches per second (950 mm/s) and the fast slew speed is 71 inches per second (1,800 m'm/s).
Comparator 13, FIG. 3 comprises resistors R R and R connected as shown. The comparator receives the reference voltage V on lead 12 and delivers the control voltage V on lead 15, which is the input to amplifier 16, represented in FIG.
3 by its input resistance R The tachometric generator 7 is connected across leads 14 and 15 and delivers a voltage V' proportional to the rotational speed of motor 1, and, accordingly, to the feed rate of the paper web. Resistors R and R form a voltage divider so that between lead 15 and point 18 there is a tachometric voltage V, equal to: V, R, (R R,). The resistance values R and R, are chosen such that the tachometric voltage V is comparable to the reference voltage V,,; i.e., for each different reference voltage V there is a rotational speed of the tachometric generator for which V is equal to V Applying Thevenins theorem of electric circuits to the circuit comprising the tachometric generator and resistors R and R there is derived an equivalent circuit comprising an ideal voltage generator G delivering voltage V in series with a resistor R whose resistance is that of resistors R and R in parallel:
e 6 R1/ (R6 R7) Accordingly, the equivalent circuit of comparator 13 is shown in FIG. 3a, where in G is an ideal voltage generator providing the reference voltage V and R' is a resistance equal to the sum of the resistances of resistor R and the portion R of 1 potentiometer R included in the circuit P. The control voltage V is the voltage developed across resistance R The current I in the equivalent circuit of FIG. 3a is given by: R" 1 eq 's c) I Since V =R I, the equation may be written as:
V V =[(R +R' +R R V =KV =V' where K is a constant and V' is a fictitious signal voltage, proportional to control voltage V,.
Thus, waveforms of FIG. 2 are valid even if, in place of the voltage V' of generator 7, the effective voltage V is considered, and if, in place of the control voltage V the fictitious signal voltage V' is taken into account, because the voltage V is proportional to voltage V and voltage V' is proportional to voltage V This requires only changing the scale of waveforms a and 12. Moreover, for V =V V 5 =0, and
The bidirectional amplifier 16 of FIG. 4 provides the control current to motor 1. Amplifier 16 comprises a voltage preamplifier including two differential amplifiers and a final stage, which include transistors T T T T and T and a current amplifier including a first stage which uses complementary transistors T and T a second stage which uses non-complementary transistors T and T and a final stage which uses two parallel-connected power transistors T and T for the positive output and two parallel-connected power transistors T and T for the negative output.
The first differential amplifier comprises the NPN transistors T and T The collectors of transistors T and T are supplied from the stabilized voltage source VA, through the respective resistor R and variable resistor R The emitters of transistors T and T are connected to the collector .of a transistor T whose emitter is connected, in turn, through a resistor R to the stabilized negative voltage source VA. The stabilized voltage sources +VA and VA are obtained respectively from two non-stabilized supply voltages V and V, applied to the respective supply terminals 33 and 34. These two supply voltages are substantially equal in amplitude and are symmetrically connected with respect to a reference voltage, which usually is the ground voltage.
Stabilization of the voltages VA and VA is provided by stabilizing circuits comprising the respective Zener diodes Z and Z and resistors R and R arranged according to wellknown techniques.
A Zener diode Z is connected between the emitter of transistor T and one end of resistor R thereby maintaining, in cooperation with resistor R the base of transistor T at a constant voltage with respect to the stabilized negative voltage VA. Thus, the current flowing through resistor R is maintained at a constant value and, consequently, the sum of the currents flowing rhough transistors T and T is held constant.
The base of transistor T is connected through a resistor R to input lead 15, on which the control voltage V is supplied. The base of transistor T is connected to a point 35. Point 35 is the central point of a voltage divider comprising resistors R and R one end of such voltage divider being grounded and the other end being connected to a terminal 17, which supplies motor 1. As it will be explained hereafter, a feed-back effect is thereby obtained.
When motor 1 is at rest, and no current flows therethrough, both terminal 17 and point 35 are at ground voltage (0 v). If input lead'15 is also at 0 v., the same amount of current must flow through transistors T and T Therefore, if R is equal to R' the collectors of transistors T and T are at the same voltage. This balanced condition can be achieved by a fine adjustment of variable resistor R if it is necessary to compensate for differences in the intrinsic resistance of the transistor. However, such differences usually will be very small, inasmuch as transistors T and T are matched to have equal characteristics, to the extent possible.
The collector voltages of transistors T and T are applied to the respective bases of PNP transistors T and T which form the second differential amplifier. The emitters of transistors T and T are connected together and to one terminal of a resistor R which is supplied at its other terminal from the positive stabilized voltage source +VA. The collector of transistor T is grounded. The collector of transistor T is connected, through a resistor R to the negative stabilized voltage source VA. This second differential amplifier is symmetrically driven by the output signals of the first differential amplifier. The employment of transistors of opposite conductivity type for the first and second differential amplifiers substantially reduces, through this compensation, the effect of temperature drift.
The collector of transistor T,;, is also connected to the base of transistor T The emitter of transistor T is connected to the stabilized negative voltage source VA. The collector of transistor T is supplied from the stabilized positive voltage source +VA through a resistor R and a diode D.
The amplifier comprising transistor T is the final stage of the voltage preamplifier and is provided with output points 36 and 37, which differ in voltage by the drop through Diode D. In the quiescent condition; i.e., in the absence of an input control voltage V the voltages at points 36 and 37 are balanced with respect to the ground. In this balanced condition the voltage at point 36 is slightly positive and the voltage at point 37 is slightly negative.
When a positive control voltage is applied to input lead 15, the conduction of transistor T increases and correspondently the current flowing through transistor T decreases. The voltage of the collector of transistor T and of the base of transistor T decreases, and the voltage of the collector of transistor T and of the base of transistor T1,; increases. The resistance of transistor T and, therefore, the voltage drop between its emitter and collector increases, whereby the voltage of the base of transistor T decreases. Therefore, current flowing through transistor TH decreases. whereupon the voltages of points 36 and 37 increases. Conversely, when a negative control voltage is applied to input lead 15. the voltages of points 36 and 37 decrease. However, the difference between the voltages of points 36 and 37, being equal to the p r s d siegtniqssnmi i w ate ably:
The above-described voltage preamplifier is followed by a current amplifier. The first stage of this current amplifier comprises a pair of complementary transistors T and T transistor T being, for example, of the NPN type, and transistor T being of the PNP type. The collector of transistor T is connected to the positive stabilized voltage source +VA through a resistor R and its emitter is connected to a point 38. The collector of transistor T is connected directly to the negative stabilized voltage source VA, and its emitter is connected to point 38 through a resistor R The voltages of points 36 and 37 are applied to the bases of respective transistors T and T In the absence of an input control voltage V both of transistors T and T are in a state of low conduction; i.e., both are close to cutoff. When a positive control voltage is applied to input lead 15 both points 36 and 37 change positively, as described previously herein. Because transistors T and T are of opposite conductivity types, transistor T becomes more conductive and transistor T becomes less conductive.
The collector of transistor T is connected to the base of transistor T The emitter of transistor T is connected to the base of transistor T Transistors T and T are of the PNP type and, with resistors R R R and R form an amplifier wherein each transistor is connected as an emitter follower. Such amplifier provides a substantial amplification of the output current.
Transistors T and T drive respectively a pair of transistors T and T and a pair of transistors T and T Each of transistors T T T and T with respective sets of resistors 21, R28 29; 30 31, 32; 33, 34 35; and 36, 31 R forms an emitter follower circuit. The emitter follower comprising transistor T is in parallel with the emitter follower comprising transistor T both such emitter followers being supplied by the positive supply voltage +V. The emitter follower Transistor T is in parallel with the emitter follower comprising transistor T both such emitter followers being supplied by the negative supply voltage V. In absence of an input control voltage V each of transistors T T T and T is in a state of low conduction, being close to cutoff, so that only a relatively small current flows through these transistors from terminal 33 to terminal 34, point 38 being at v.
When a positive control voltage is applied to input lead 15, the base of transistor T becomes more positive and transistor 15 becomes more conductive, whereas although the base of transistor T also becomes more positive, the conduction of transistor T decreases. Consequently, point 38 becomes positive and causes a positive increase of the voltage at point 35, the base of transistor T Thus, the difference between the currents through transistor T T decreases. Thus, a negative feed-back effect is provided, with its well-known advantages of greater stability and less sensitivity to noise.
The increase in conduction of transistor T and the decrease in conduction of transistor T cause a respective decrease of the base voltage of transistor T and increase of the base voltage of transistor T Thus, transistor T becomes more conductive and transistor T less conductive. Under these conditions, the decreased voltage of the emitter of transistor T causes a conduction of transistors T and T to increase, whereas the increased voltage of the emitter of transistor T causes the conduction of transistors T and T to decrease. Transistors T and T thereby deliver a greater positive current and transistors T and T a lesser negative current to terminal 17.
As a consequence, for a positive control voltage the motor connected to terminal 17 receives a positive current and is accelerated as required. In the opposite case; i.e., wherein a negative control voltage is applied to lead 15, a negative current is supplied to the motor, with its consequent braking effect.
Since terminal 17 is directly connected to point 38, there is no need to stabilize the supply voltage in the current amplifcation stages which follow complementary transistors T and T In fact, the stabilization of the voltage at points 31 and 32, ensures that the voltage of point 38 is affected only by the control voltage at input lead 15 and not by accidental fluctuation of the supply voltages +V and V.
Accordingly, the possible fluctuations of the non-stabilized voltage supplying the following stages cannot influence the voltage of point 17, which supplies motor 1. Since the current required for the stage with the complementary transistors T and T and the preceding stages is substantially lower than that required for the following power stages, a remarkable saving in cost and dimensions of the components of the stabilizing circuit is attained, relative to that which would be required for stabilizing the voltages +V and V provided at terminals 33 and 34.
A satisfactory result, with even a lower cost of the stabilizing components, may be provided by the arrangement illustrated in FIG. 5. The circuit of FIG. 5 differs from that of FIG. 4 in that the supply voltage for the complementary transistors T andv T is also not stabilized, but only the supply voltage for the preceding stages. By this arrangement, the stabilized voltages +VA and -VA, obtained by use of resistors R and R and Zener diodes 2. and Z are present at points 40 and 41, whereas at points 31 and 32 the non-stabilized voltages +V and V are present.
The current to be stabilized is further reduced and an additional saving thus results. In this instance the voltages of points 36 and 37, and therefore the voltages applied to the bases of transistors T and T are independent of fluctuations of voltages +V and V. The effect of such fluctuations on the voltage of point 38, however, although theoretically not zero, is effectively negligible. In fact, this effect is reduced to the changes in voltage drop across the base-emitter junctions of transistors T and T due to changes in the current flowing through these junctions as a result of such voltage fluctuations.
1. A device for controlling paper feed in a printing apparatus, comprising a low-inertia motor, a tachometer device for delivering a tachometric voltage proportional to the paper feed speed, a pulse generator device for delivering a pulse each time the paper is moved a distance equal to a line pitch, a logical control device having inputs to receive command signals and pulses generated by said pulse generator device, a selectively controlled reference voltage generator, for delivering a reference voltage in response to a set of control signals generated by said logical control device according to the command signals and pulses received thereby, said reference voltage generator comprising first, second and third transistors having the collector thereof supplied from a common voltage source through respective first, second and third resistors, the bases of said transistors, being connected to respective first, second and third input terminals, the emitters of said transistors being directly connected to ground, the collectors of said transistors being further connected to one electrode of respective first, second and third diodes, the other electrodes of each of said diodes being connected to one fixed terminal of a potentiometer, the other fixed terminal of said potentiometer being connected to ground, and the movable tap of said potentiometer being connected to the output terminal of said reference voltage generator, a comparing device for comparing a voltage proportional to said tachometric voltage and said reference voltage and for generating a signal voltage having an amplitude depending on the difference between said reference voltage and said voltage proportional to the tachometric voltage, and a bidirectional amplifier for controlling the rotational speed of said low-inertia motor by means of a supply current controlled in amplitude and direction by said signal voltage,
said reference voltage generator operating to deliver to said output terminal a particular reference voltage, selected among a plurality of predetermined reference voltages, in response to the patterns of signals when appropriate patterns of signals are applied by said logical control device to said reference voltage input terminals.
2. The device of claim 1, wherein said comparing device comprises first and a second series connected resistors connected between a first input terminal and an output terminal, a third resistor connected between the point common to said first and second resistors and a second input terminal, said tachometric device applying between said output terminal and said second input terminal a tachometric voltage proportional to the rotational speed of said motor, said first input terminal being directly connected to the output terminal of said reference voltage generator.
3. Apparatus for controlling the slewing of a print-receiving member to a precise final position in a high-speed printer in response to input command signals representing the number of line pitches through which said member is to be slewed, comprising: an electric motor for slewing said print-receiving member through a printing position, means for sensing the slewing of said print-receiving member and for delivering a first type signal representing said slew speed and a pulse each time said print-receiving member moves a distance of one line pitch through said printing position, first control means responsive to the receipt of said input command signals for generating a reference signal having a first value representative of a predetermined slew speed, said first control means comprising first, second and third transistors having the collector thereof supplied from a common voltage source through respective first, second and third resistors, the bases of said transistors, being connected to respective first, second and third input terminals, the emitters of said transistors being directly connected to ground, the collectors of said transistors being further connected to one electrode of respective first, second and third diodes, the other electrodes of each of said diodes being connected to one fixed terminal of a potentiometer, the other fixed terminal of said potentiometer being connected to ground, and the movable tap of said potentiometer being connected to the output terminal of said first control means, second control means responsive to said input command signals and to said pulses to generate a second type signal when said print-receiving member requires slewing only through a predetermined number of remaining line pitches, said first control means being responsive to said second type signal for changing said reference signal to a second value representative of a deceleration of said motor, means for delivering a third type signal representing the algebraic difference between said reference signal and said first type signal, and means responsive to said third type signal to control the speed of said motor.
4. Apparatus for controlling the slewing of a print-receiving member to a precise final position in a high-speed printer in response to input command signals representingthe number of line pitches through which said member is to be slewed comprising: an electric motor for slewing said printreceiving member through a printing position, a speed-sensing member for sensing the speed of slew of said print-receiving member and for delivering a first type signal representing said slew speed, a line pitch sensing member for sensing the slewing of said print-receiving member and for delivering a pulse each time said print-receiving member moves a distance of one line pitch through said printing position, first control means responsive to receipt of said input command signals for generating a reference signal having a first value representative of a predetermined slew speed, said first control means comprising first, second and third transistors having the collector thereof supplied from a common voltage source through respective first, second and third resistors, the bases of said transistors, being connected to respective first, second and third input terminals, the emitters of said transistors being directl connected to round, the collectors of said transistors being urther connec ed to one electrode of each of said diodes being connected to one fixed terminal of a potentiometer, the other fixed terminal of said potentiometer being connected to ground, and the movable tap of said potentiometer being connected to the output terminal of said first control means, second control means responsive to said input command signals and to said pulses to generate a second type signal when said print-receiving member has been slewed through the number of line pitches represented by said input command signals less a predetermined number of line pitches, said first control means being responsive to said second type signal for changing said reference signal to a second value representative of a deceleration of said motor, means for comparing said reference signal and said first type signal for delivering a third type signal representing the algebraic difference between said reference signal and said first type signal, and means responsive to said third type signal to control said motor to accelerate said print-receiving member to said predetermined slew speed after said apparatus receives said input command signal and, after said second type signal has been generated, for decelerating said print-receiving member to stop after having been slewed through the precise member of line pitches represented by said input command signals.