US3740634A - Apparatus for controlling the feeding of paper in high-speed printers - Google Patents

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 speedproportional 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

United States Patent 1 1 Bonzano 1111 3,740,634 June 19, 1973 1 1 APPARATUS FOR CONTROLLING THE I FEEDING OF PAPER IN HIGH-SPEED PRINTERS [75] Inventor:

[73] Assignee: Honeywell Information Systems Italia S.p.A., Milan, Italy Giorgio Bonzano, Caluso, Italy [62] Division of Ser. No. 54,815, July 14, 1970, Pat. No.

3,450,973 6/1969 Tobey 318/345 3,523,228 8/1970 Currie 318/681 3,599,063 8/1971 Nanai 318/327 Primary ExaminerBernard A. Gilheany Assistant Examiner-Thomas Langer Attorney-George V. Eltgroth, Lewis P. Elbinger and Aubrey C. Brine [57] ABSTRACT Apparatus for controlling the paper feeding in printing 3,656,041 apparatus, wherein the feed motor speed is controlled 52 US. Cl. 318/345 318/681 by f effect of Speed-Space detector 51 1111.11 "1102;, 5/16 whse speedfpmpomonal "P s and Said [58] Field of Search 318/327 345 331 Pulses are P predtermmed Pulse 3 8 her, and wherem the results of sa1d comparison are employed in combination to provide a suitable paper feed [56] References Cited power control through a bidirectional amplifier which UNITED STATES PATENTS does not requ1re a stabllized power supply.

3,538,353 11/1970 Hanger 318/345 2 Claims, 8 Drawing Figures Patented June 19, 1973 5 Sheets-Sheet 1 MPLIFIER VOLTAGE COMPARATOR REFERENCE VOLTAGE LOGIC DEVICE\ .21, w

GENERATOR Patented June 19, 1973 5 Sheets-Sheet 3 m QE ll l.l.l l||| IIIL Patented June 19, 1973 5 Sheets-Sheet 4 EMM Patented June 19, 1973 5 Sheets-Sheet 5 APPARATUS FOR CONTROLLING THE FEEDING OF PAPER IN HIGH-SPEED PRINTERS This is a division, of application Ser. No. 54,815, filed July l4, 1970, now U.S. Pat. No. 3,656,041.

BACKGROUND OF THE INVENTION This invention relates to apparatus for controlling the paper feeding in high-speed printers, particularly in printers employed in information processing 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 in tegral 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 be tween portions of printed text.

Apparatus is known for precisely controlling the position of the paper at the end of each line feed or slew such pin-and-ratchet devices, gears, and the like. However,.devices are costly and are subject to considerable operation. This usually comprises mechanical means,

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 am .plifiers suitable for 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 constant speed, and

a third stateof fast deceleration (braking). In the first state the controlling amplifier delivers a large current of predetermined polarity. in the'second state .the cur-- rent 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 deliv- 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 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,

' FIG. 4 is a schematic diagram of the bidirectional amplifier of FIG. 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 ortational 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. Therefore, photocell 6 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-bystep 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., l,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 l3. Comparator l3 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 a control 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 16 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 supplies 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 voltage V; and illustrate the current delivered to the motor, for the example of a fast slewing. In this example, respondingto 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 (waveform c).

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 output 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 thenumber 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 thebraking 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 II, FIG. 3, comprises three transistor 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 connectedto 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. Terminals 21, 22, and 23 receive control signals from logical device 8, which correspond to the required referencevoltage to be delivered. The control signals on terminals 21, 22, and 23 represent binary values, the binary I being represented by a positive voltage (for example instance +5V), and the binary 0 being represented by 0v.

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 0v, and, consequently, point 25 drops to 0v. Accordingly, reference voltage V,, on lead 12 is at 0v. 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 1 signals, transistor T, becomes nonconductive. 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 step-by-step feeding.

If a binary 0 signal is applied to both input terminals 21 and 22, transistors T and T become nonconductive. 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 I l l O Step-by-step 0 I I V,

Slow slew 0 0 v l V,

Fast slew 0- I 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 terminalsare 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. I

A set of suitable values for these resistances is, for example, the following:

ratios between reference voltages and corresponding I speeds are:

V /V 1.69 Vii/V 3.24

If the step-by-step feeding speed is, for example, 22 inches per second (560 mm/s) the slow slew speed is appr. 37 /2 inches per second (950 mm/s) and the fast slew speed is 71 inches per second (1,800 mm/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 amplitier 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;

ea e r/ 0 1) 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 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:

V V =(R R' R I Since V R 1, the equation may be written as:

:where K is a constant and V,- is a fictitious signal voltage V and voltage V, is proportional to voltage V,.

This requires only changing the scale of waveforms a and b. Moreover, for V =V V,=0, and

I The bidirectional amplifier 16 of FIG. 4 provides the control currentto 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 resistor R and R arranged according to well-known 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 through 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 pointof 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 (v). If input lead 15 is also at 0v., 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 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 5, 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 form the stabilized positive voltagesource +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 voltageat 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 T 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 T decreases, whereupon the voltages of points 36 and 37 increase. Conversely, when anegative 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 drop across diode D, does not change appreciably. 1

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 0 and a pair of transistors T and T Each of transistors T T T and T with respective sets of resistors R R R R R R R R R and R R R 8 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 21 and T is in a state of low conduction, being close to cutoff, so that only a relatively small current flows 35, the base of transistor T Thus, the difference between the currents through transistor T and 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 the 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 todecrease. 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 cur- -rent 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 amplification 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 nonstabilized 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 and 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 Z, and Z are present at points 40 and 41, whereas at points 31 and 32 the non-stabilized voltages +V and -V are present.

I 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.

I claim:

1. A bidirectional amplifier provided with an input terminal directly connected to the output terminal of a voltage comparator, comprising a bidirectional voltage preamplifier fed by first and second stabilized voltage sources, said first and second voltage sources having equal amplitudes and opposite polarities with respect to a ground reference voltage, a bidirectional current amplifier driven by said voltage preamplifier through first and second connecting terminals, wherein a first stage of said bidirectional current amplifier comprises a first transistor of NPN type having the collector thereof connectedto a positive supply voltage through a first resistor and the emitter thereof connected to an output terminal and a second transistor of PNP type said first transistor being connected to the base of a third transistor connected in a first emitter follower circuit, said first emitter follower circuit being connected between said positive supply voltage and said output terminal, the emitter of said second transistor being connected to the base of a fourth transistor connected .in a second emitter follower circuit, said second emitter follower circuit being connected between said output terminal and said negative supply voltage, said first and said second emitterfollower circuits each driving at least one a power emitter follower circuit. said power emitter follower circuits being symmetrically connected between said positive and negative supply voltages and said output terminal; said output terminal being directly connected to one input terminal of said low-inertia motor, a second input terminal of said lowinertia motor being connected to said ground reference voltage. v

2. The bidirectional amplifier of claim 1 wherein the supply voltage of said first stage of said current amplifier is not stabilized.

Claims (2)

1. A bidirectional amplifier provided with an input terminal directly connected to the output terminal of a voltage comparator, comprising a bidirectional voltage preamplifier fed by first and second stabilized voltage sources, said first and second voltage sources having equal amplitudes and opposite polarities with respect to a ground reference voltage, a bidirectional current amplifier driven by said voltage preamplifier through first and second connecting terminals, wherein a first stage of said bidirectional current amplifier comprises a first transistor of NPN type having the collector thereof connected to a positive supply voltage through a first resistor and the emitter thereof connected to an output terminal and a second transistor of PNP type having the emitter thereof connected to said output terminal through a second resistor, and the collector thereof connected to a negative supply voltage, said positive and negative supply voltages having substantially equal amplitudes with respect to said ground reference voltage; the base of said first transistor being connected to said first connecting terminal of said preamplifier and the base of the second transistor being connected to said second connecting terminal of said preamplifier, a diode suitably connected across said connecting terminals to provide a substantially constant voltage difference therebetween; the collector of said first transistor being connected to the base of a third transistor connected in a first emitter follower circuit, said first emitter follower circuit being connected between said positive supply voltage and said output terminal, the emitter of said second transistor being connected to the base of a fourth transistor connected in a second emitter follower circuit, said second emitter follower circuit being connected between said output terminal and said negative supply voltage, said first and said second emitterfollower circuits each driving at least one a power emitter follower circuit. said power emitter follower circuits being symmetrically connected between said positive and negative supply voltages and said output terminal; said output terminal being directly connected to one input terminal of said lowinertia motor, a second input terminal of said low-inertia motor being connected to said ground reference voltage.

2. The bidirectional amplifier of claim 1 wherein the supply voltage of said first stage of said current amplifier is not stabilized.

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