DE2813855A1 - Positioning system for transport mechanism - uses difference between nominal and actual values of pulse period for motor voltage control - Google Patents

Abstract

The transport mechanism is driven by a DC motor and moves a recording medium. It has a pulse generator coupled with the motor shaft; a counter storing the distance to the target position and a speed controller for the DC motor, whose reference element delivers a control variable depending on the counter reading. Pulses from the pulse generator are applied to a time measuring circuit which generates an actual value corresponding to the period of these pulses. The difference between the control variable which corresponds to the nominal period duration, and the actual value is the control deviation controlling the DC motor voltage.

Description

To an object, for example a receipt

within a business machine, quickly and with great accuracy to adjust to a desired target position have been common in the past Stepper motors used. Such engines and those used to operate them required control circuits are not only relatively expensive, but also wise also has the disadvantage that rapid starting and stopping are not easy is possible because they have a very strong tendency towards harmonics.

For this reason, the drive must be precisely positioned Objects often also use DC motors. For example, it's off DE-OS 22 46 543 a device for braking a fast along a path Known in a defined end position to be moved belt, in which one in his Speed controllable DC motor is used. In this device is an encoder for a signal corresponding to the respective speed of the belt and an encoder for one of the path lengths to be covered until the end position is reached corresponding signal provided. This path length encoder is a memory for the Relationship between the permissible speed values and the speed up to which they are reached assigned to the end position path lengths to be covered and by means of a comparison device is the signal for the respective speed of the belt with a signal for compared the permissible speed. The motor is then supplied with current according to the result of this comparison.

In such a drive system in which a time-optimal braking according to a predetermined function of the speed profile as a function of the distance to the target while at the same time maintaining tight tolerance limits the Targeting accuracy should be relatively expensive-servomotors-in-the-kind of Bell and disc motors required. '.

-The-: The invention is therefore based on the object of a positioning control system for a DC motor-driven transport mechanism of the aforementioned Kind of like that. 'to design') that also relatively simple DC motors. with Permanent magnet excitation and iron runners, such as those used in the toy industry be used r. 'can be applied without compromising the positioning accuracy as well with changing load and changing environmental conditions.

This object is achieved by the invention defined in claim 1 solved. Appropriate refinements of the invention emerge from the subclaims and from the exemplary embodiments described below.

A major advantage of the invention.

Positioning system does not only consist in the fact that there is an additional tachometer generator to determine the respective rotational speed of the motor is unnecessary, but that. by regulating the. Pulse period time instead of the speed of the control loop receives a non-linear behavior, which has the effect that the Gain of the control loop increases as the target position is approached, whereby greater accuracy is achieved.

Another advantage is that due to the special function the default values for the pulse period time the motor is switched off shortly before the actual target position can be carried out practically in the de-energized or de-energized state can, so that the engine coasting down from a minimum top speed to zero speed - only through the system friction and not through electrodvnamic Shutdown processes in the engine is impaired.

Some exemplary embodiments of the invention are illustrated below of the drawings.

- Continued on page 11 - In these shows: Fig. 1 shows a basic, greatly simplified representation of a document transport device a line printer as an application example for the positioning control system according to the invention; Fig. 2 shows a basic representation of a control loop as it is in the inventive Positioning control system can be used; Fig. 3 shows a modification of the in Fig. 2 shown control loop, which is preferably used in the inventive positioning control system is used; Fig. 4 is a block diagram of a first embodiment of the Positioning control system according to the invention in combined analog and digital Circuit technology; FIG. 5 shows signal forms as they are in the exemplary embodiment shown in FIG appear; 6 to 9 various diagrams showing the pulse time, the speed and the motor voltage as a function of the distance to the target position or in Represent dependence on time; 10 shows an embodiment of a driver circuit for the DC motor to be controlled; 11 is a block diagram of a second embodiment the positioning control system according to the invention in digital circuit technology; 12 shows count values or waveforms as they are in the exemplary embodiment shown in FIG appear; 13 is a diagram showing the setpoint and actual value of the pulse period time depending on the distance to the target position for the second embodiment illustrates; and FIG. 14 shows a greatly simplified block diagram of a third exemplary embodiment of the positioning control system according to the invention using a microcomputer system.

With reference to Fig. 1 is first an application example for the invention Positioning control system described. Fig. 1 illustrates in a greatly simplified Form a transport device for a sheet-shaped recording medium 1, e.g. B. an account card or an invoice form, which is part of a booking engine can be. The recording medium is in relation to a printing station, which by a platen 2 and printhead 3 is illustrated to position.

The print head 3, which can be, for example, a wire matrix print head can, can by not shown drive means in the direction of the printing roller axis, i.e. moved in the direction of arrows 4 to print a line on the form.

To the form 1 in relation to the printing station on a certain line to set or to break a line after printing a line To be able to make, it is necessary to move Form 1 in the direction of the double arrow 5 to move and to be able to stop at a precisely defined point. This is the form 1 with its lower (left in Fig. 1) edge in a clamping device 6 clamped, the two ends of which are firmly connected to an endless toothed belt 7 each are. Each of the two toothed belts 7 runs over an idle roller 8 and each via a drive roller 9. The two drive rollers 9 are fixed with a Connected to the drive shaft 10, on which a drive pulley 11 sits, which via a further toothed belt 12 of one with the shaft 14 of the motor 15 firmly connected toothed disc 13 is driven. The two Toothed pulleys 11 and 13 are preferably dimensioned so that they are a reduction gear form.

On the other end of the motor shaft 14 there is a timing disk 16, which on their circumference with equally spaced clock markings is provided. A fork light barrier designed as a fork light barrier acts with the timing disk 16 Sensor 17 together, which on its output lines 18 when rotating the engine emits pulses corresponding to the sequence of the clock markings. These impulses will be both for distance measurement and for the measurement of the rotational speed vice versa proportional pulse period is used, as will be explained in more detail later is described. In order to be able to determine whether the motor 15 is forward or backward is running, a further clock track can be provided on the clock disk 16, the cooperates with another sensor. The line markings of this further The clock track should be slightly offset from the markings on the first clock track be, for example by a quarter division. The same effect is achieved when two slightly offset sensors work together with a single clock track. The output lines 18 of the sensor 17 and the connection lines 19 of the motor "15 lead to the control circuit still to be described in detail.

The DC motor 15 used for the drive can be a relatively be a simple standard motor with permanent magnet excitation, collector and iron rotor. Such motors have relatively high values for the rotor moment of inertia and the inductance and thus also for the mechanical and electrical time constants and show because of their friction losses on the collector and in the sintered spherical bearings as well due to their pronounced magnetic reluctance torques, overall unfavorable properties from a control point of view.

Nevertheless, it is by means of the positioning control system according to the invention possible the form 1 with the engine. 15 of the type mentioned and the one described Transport device relatively quickly and at high speed to the desired Position. Of course, higher quality DC motors, such as bell and disc motors can be used.

In Fig. 2 is a basic block diagram for the simplest Embodiment of the positioning controller according to the invention shown. The motor 15 represents a non-linear transfer element since it controls the voltage applied to it UM into one that is inversely proportional to this voltage and also to the speed of the motor Pulse time or pulse period duration TE converts. This pulse time TE is the period duration the pulses scanned by the clock disk 16 by means of the sensor 17. One himself possibly reducing the motor voltage by reducing the speed corresponds to a inversely proportional increasing pulse period time TE. This actual pulse period time TE is compared with the respective nominal period duration TF, that is to say the latter is subtracted from the former to form the difference T. This difference is positive if the actual period TE is greater than the target period TF, which means that the engine is running too slowly and has to be accelerated. The difference ßT is thus in a linear transmission element 20 within a range # Tmax converted into a proportional voltage UM.

If the difference #T is negative, which means that the motor is too fast runs and therefore has to be braked, then converts the linear transmission link 20 this negative difference into a correspondingly negative and braking effect Motor voltage UM. If the difference T is equal to or greater than a certain one to be determined maximum difference jUmaX, then depending on the sign of this difference the motor either the maximum possible positive or the maximum possible negative Voltage supplied.

The following equations apply = TE - TF 'where in the case tT is converted proportionally into a motor voltage UM. It applies Outside the proportional range UM = + Umax for #T> 0 UM = - Umax for #T <0 The angular speed (#) of the motor is set according to the difference between the applied voltage UM and a torque-proportional voltage UV according to the following equation, where KE is the The voltage constant of the motor means: #. KE = UM - UV The following relationship exists between the angular velocity LJ and the pulse period time TE: where N is the number of slots or lines in the timing disc. From equations (1) and (2) it follows: This equation shows the non-linear relationship between the actual period TE and the target period TF. The gain GR of the control loop according to the invention is therefore not a constant as in linear systems, but is obtained for the gain The gain GR of the control loop thus increases with increasing values for TE, ie with decreasing speed and thus with approaching the target position, which has a favorable effect on the control behavior. Although the stability of the control loop deteriorates with increasing gain, on the other hand the control error decreases.

Since the gain decreases as the speed increases, the The tendency of the system to overshoot when the motor is started is reduced. With decreasing Speed, i.e. also during the positioning process, the gain of the system increases at. This eliminates the influence of disturbance variables that affect the speed can, greatly reduced, which has a favorable effect on the positioning accuracy. The simultaneous deterioration in stability can have practically no effect, if the braking process runs sufficiently quickly, because the control loop is rocking of vibrations takes time. As can be seen from the diagram shown in FIG is, can in the positioning control system according to the invention ever depending on the distance to the positioning target SIII, three different path and functional areas a distinction can be made, which represent the abscissa of the diagram. The area I is the area that is more than the distance I from the target position SIII away.

The area II extends between the points SI and the point SII, in which the motor is switched off or short-circuited and sets the actual positioning area. Area III is the target area within which is the actual target position SIII, which is the final speed VE from point SII in the de-energized state of the motor with a positioning accuracy is started by + d s.

On the ordinate of the diagram shown in Fig. 6 is the pulse time applied. The full curve represents the target value for the pulse duration TF, which is constant in area I (TFI) and in area II the one shown shows a disproportionate course (TFII). The actual pulse period would be accurate follow this curve, then this would correspond to a motor voltage UM = O V. The two dash-dotted lines around the aforementioned curve profile of the target pulse period time TF, which are denoted by + Umax and - Umax, define the proportional Control range.

In range I, the limits of the proportional control range are closer on the setpoint curve than in area II. This means that in the case of the Example in area I the gain GRI is greater than the gain GRII im Area II. This is useful or necessary if the engine is fast, for example aperiodically, accelerated to its normal speed and then operated constantly at this speed for a certain duration or distance shall be.

This is necessary, for example, when the engine powered transport mechanism is also used to transport magnetic account cards, since a speed that is as constant as possible for the recording and reading operations is needed. For the positioning accuracy, the functional area I is relative uncritical. If therefore no precisely defined or constant normal speed is required, the pulse period time can be regulated within this range be waived.

Depending on the distance to the destination, i.e. depending on the location of the starting point in range I, the motor reaches the range with a certain pulse period time II, as shown by the dashed lines in FIG. Within of area II, the so-called positioning area, the motor is now in accordance with a path-dependent control characteristic to a minimum final speed VE delayed, where the motor voltage is the difference between actual-> E and target pulse period time TF corresponds, and as a result can also assume negative values. The control characteristic shows an approximately logarithmic curve and is used for an optimal braking process through mathematical analysis of the control dynamics for the respective application determined, in such a way that an approximately linear decrease in the motor voltage occurs until the value zero at point SII. As mentioned earlier, this point is the Beginning of the target range and at this point the motor voltage is switched off. The control characteristic and the gain GRII are also determined so that the engine from the maximum speed Vmax out on the regulated final speed VE is braked so that this final speed VE despite scattering of the machine parameters and components and despite existing faults varies little, that the engine does not stop before the goal, that the run-in the target is done with as little vibration as possible and that finally the positioning times are minimal.

On a regulation of the motor speed down to zero speed, what at first glance suggests the best positioning results will no longer exist dispensed with the following reasons: First, leave the for the use of the invention Positioning control system preferably used permanent magnetic direct current motors because of their pronounced reluctance torques and commutation problems, such as periodic Resistance and inductance changes, no regulation down to zero speed, since these motors run unevenly below a limit value for the speed, which the control system cannot compensate due to the time constants of the motor. A deterioration in the positioning accuracy would therefore be the result.

Second, a pulse time control up to zero speed is not possible because the pulse time there assumes an infinitely large value. Therefore will the set or reference impulse time is only defined up to the limit value TFmaX and the Actual pulse time measurement remains limited to values less than max.

In order to take this last-mentioned fact into account, the The control loop shown in FIG. 2 is so unshaped that the one shown in FIG Control loop results.

This control loop shown in Fig. 3 differs from that shown in Fig. 2 in that by inserting transducer members 21 and 22 the target pulse period time TF and also the actual pulse period time TE in corresponding Values TF * or TE * can be transformed in the following way: T * = T -T F max F and correspondingly TE * = Tmax TE The difference a T is now obtained by subtraction of the actual value TE * from the target value TF * t, as can also be seen from FIG. 3 is. Namely, the following relationship applies: = = TE - TF = TF * T TE * that shown in FIG. 6 Unregulated target area III is, as already mentioned, defined in that -'der Motor it with a final speed determined by the pulse time control VE reached and within this range after switching off the motor voltage the system friction is braked to a standstill. Area III is in his Size dimensioned so that the engine is saved even in the worst case due to its kinetic and possibly still existing electrical energy as a function from the system friction in the required tolerance band for the target position SIII + d 5 runs in aperiodically and is held there by the static friction.

Before now the invention with reference to some embodiments in detail is described, reference should be made to two essential features through which it is ensured that the positioning control system according to the invention also then works safely and satisfactorily when from a short distance to the target is started and when extremely unfavorable conditions exist.

When the target is approached, the maximum voltage effective on the motor becomes reduced. This means that a start is also possible immediately in front of finish area III, without the engine overshooting the target. The voltage is restricted to such values that in the worst case, i.e. when maximum system friction occurs, it is still possible for the motor to start. In what way this voltage restriction will be described in detail later.

To prevent the engine from malfunctioning already the target area comes to a standstill, the Motor voltage increases linearly with time if the actual pulse time TE of the motor is a certain one Exceeds limit value TG. This accelerates the engine again.

A first exemplary embodiment will now be described with reference to FIGS of the positioning control system according to the invention described in detail. at the embodiment shown as a block diagram in FIG. 4 takes place Digital distance measurement and analog recording of the pulse period time. There will be in it uses the following function blocks: In a line counter and decoder 25 is interlaced via a line 23 Form a count 5 entered, which corresponds to the distance c to the target position. In the embodiment described, every 1/6 inch (approx. 4 mm) resolved into 40 counting pulses. To make sure that the counter reading is always remains positive, the target position SIII is placed on the count 5, with the permissible positioning tolerance should be + 3 counting pulses.

For a jump to be carried out from one line to the Counter 25 a count 5c of 45, for 2 lines a count of 85 accordingly and enter a count of 125 for 3 lines. The size or

The capacity of the counter depends on the maximum to be positioned Path. In the exemplary embodiment described, a 12-stage counter is used, which thus a positioning of a maximum of 400 mm path length allows. In one more later In the manner described in more detail, the counter is set according to the amount covered by the engine Counted way down.

A decoder contained in the counter block 25 determines if the counter reaches a count SD d 128 and a count SD z 8. Upon reaching of the count 128 is a digital-to-analog converter described in more detail below 26 put into operation. When a count value of 5D = 8 is reached, a line 25a, the motor voltage by means of a motor control circuit 31, which will be described in more detail later UM switched off.

The already mentioned digital-to-analog converter 26 converts the from Counter block 25 supplied count values 128 to O into corresponding voltage values U1 around. This dem Count value of the counter proportional voltage values U1 are applied to a function generator 27, which corresponds to the desired path-dependent braking function generates a voltage U2, which is the reference variable for the control loop described below. This voltage U2 represents represents the target value TF *, as it has already been described in connection with FIG. 3.

The mentioned voltage U2 is used together with a voltage to be described Voltage U9, which corresponds to the actual value also described in connection with FIG T * ent-E corresponds, applied to a subtraction amplifier 28, to the difference these two tensions to form. This differential voltage representing the control deviation U3 is amplified in a voltage amplifier stage 29. By setting the gain factor this voltage amplifier can influence the gain GR of the control loop.

For example, it would also be possible when moving out of the functional area III (see Fig. 6) into functional area II, i.e. when the count value is reached 128 to switch the gain from a higher to a lower value, like this has already been mentioned in connection with FIG. The sign and amount The analog voltage U4 corresponding to the control deviation is now used as a pulse width modulator 30 supplied. This pulse width modulator works with an internal triangular shape Voltage U5 with a frequency of 4kHz and that obtained by the modulation Width-modulated square-wave pulses of the frequency mentioned are now sent to a motor control circuit 31 created.

This motor control circuit 31 includes three functional blocks, viz a shutdown block 32, a forward-reverse switch 33, and a driver stage control block 34. The shutdown block 32 causes the motor voltage to be switched off when the Line 25a coming from counter and decoder block 25 signals a count value SD A 8 will. The command “start command forward - applied backward to determine whether the motor is in forward or reverse direction should run. The direction of rotation can be reversed in a simple manner by means of a logical inverse ion of the pulse width modulated signal U6.

The output from the motor control circuit 31 and possibly inverted pulse width modulated signals U6 is now sent via the driver stage control block 34 of the motor driver stage 35 supplied, which a corresponding voltage U7 to the function block symbolizing the direct current motor 15 (FIG. 1) and the load 36 creates.

The driver stage 35 is together with the motor control circuit 31 and the direct current motor 15 shown again in detail in FIG. About the both by the positive and negative half-waves of the pulse width modulated Signals U6 applied lines 31a and 31b are alternately one or the other of the two transistors T1 and T2 made conductive so that alternately each for one due to the pulse width ratio of positive and negative half-wave a certain period of time the voltage + Umax and the voltage -Umax on the winding of the DC motor arrives. The inductance of the motor winding works integrating or smoothing on the motor current.

If the width of the positive half-wave is equal to the width of the negative Half-wave or the pulse width ratio is equal to 1, which is a control deviation would correspond to zero (U3 and U4 = OV), then ~ the effect of both Voltages + Umax and Umax in the motor cancel what an effective motor voltage would correspond to zero volts.

The function block 37 contains a slotted disc provided with two tracks and two optical scanning devices or optical scanning devices cooperating with these tracks. Sensors.

The slotted disc rotates at a speed corresponding to the engine speed Angular velocity>). The signal derived from the first clock track is also included the pulse period duration TE is fed to a pulse duration voltage converter 38.

This consists of an integrator and a constant current source and is set to a constant voltage in the time sequence of the clock pulses U8max charged and then discharged linearly over time. At the end of a pulse period TE is the voltage U8 still present at this point in time to a holding circuit 39 delivered, which stores this voltage as Ug for the following pulse period and - as already mentioned - for comparison with the reference voltage U2 to the subtraction amplifier applies. If it is determined in function block 38, i.e. in the pulse duration voltage converter, that the period TE reaches or exceeds a certain limit period TG, then an FET transistor contained in said holding circuit 39 becomes conductive made, whereby the further decreasing voltage U8 during the still running.Taktimpulsbeispiel immediately the subtraction amplifier 28 is coupled, so that the motor voltage increases linearly over time and the motor is accelerated.

The signal scanned from clock track I of the slotted disc (Function block 37) and the clock signal sampled by the clock track II, the opposite the first has a phase shift of a quarter pulse period applied to a function block 40, which consists of the two mutually phase-shifted Clock signals I and II determine the actual direction of rotation of the motor and over the line 40a supplies a corresponding counting direction signal to the counter block 25. In the function block 40 also doubles the clock pulse frequency, i. e. for each clock pulse period TE, two counting pulses are sent to the via a line 40b Meter block 25 delivered.

Is the set direction of rotation by setting the forward / reverse switch 33 is set to "forward" and is also used as the actual direction of rotation in function block 40 "Forward" is determined, then this is effected via line 40a to the counter block 25 applied counting direction signal that the via line 40b to the counter block 25 incoming counting pulses increment the counter contained in this block downwards. If, on the other hand, the actual direction of rotation was determined to be "backwards" in function block 40, then a corresponding upward counting of the counter would take place. This ensures that even when an error occurs, when overshooting or when manipulating outside the line counter contained in the function block 25 always has the correct distance to the target position.

Based on the waveforms and voltages shown in FIG now again briefly the mode of operation of this exemplary embodiment of the invention explained. Waveform a in Fig. 5 represents that from track I of the clock signal slice sampled clock pulse period sequence. As can be seen from this figure, grows the pulse period duration of the individual pulse periods TEl to TE6 with time, which means that the engine speed will decrease over time. At the start each of the clock pulse period applied to the pulse-time-to-voltage converter 38 becomes this - as already mentioned - charged to the constant maximum voltage U8max, as can be seen from signal form b.

The voltage U8 is increased by discharging for the duration of one pulse period linearly reduced. A low discharge and thus a high remaining voltage U8 at the end of a period thus means a short pulse period and thus a relatively high engine speed. Each at the end of a pulse period Any voltage U8 that is still present is - as already mentioned - in the holding circuit 39 for the next I »puLsperlode and maintained as the actual value voltage Ug in the 8ub traction amplifier 28 compared with the nominal value voltage U2. This fact is shown in signal form c. The value of the stepped voltage drop Ug, for example within the pulse period TE3, corresponds to the final voltage Uß (Waveform b) at the end of the previous pulse period, namely the pulse period TE2.

over the voltage Ug iit in the waveform c with dashed lines the Boll value voltage U2 is shown. As can be seen from the waveform c, occurs a reduction in the Boll value voltage U2 after approximately half a time Pulse period TE on because - as already mentioned - the call-up of the setpoint value from function blocks 26 and 27 effecting counter 25 with opposite the clock pulse frequency is incremented downwards twice the frequency.

The difference voltage obtained by the subtraction amplifier 28 U3 is in signal form c by the double arrow within the pulse period TE3 indicated. That, by amplifying the differential voltage U3 in the voltage amplifier 29 obtained voltage U4 is in the signal form d by the dash-dotted line shown. This amplified differential voltage U4 is used in the pulse width modulator generated triangle voltage U5 into a corresponding pulse width modulated square wave signal U6 converted, which is roughly the one shown in signal form e by the driver stage 35 supplied motor voltage U7 corresponds. This pulse width modulated motor voltage U7 jumps back and forth between the voltages + Umax and - U.

max The motor current caused by this voltage is over the motor inductance is smoothed sufficiently so that on the motor depending on the duty cycle a medium voltage - Umax <UM <<+ Umax becomes effective.

Of course, it is also possible that the full voltage + Umax or - Umax takes effect on the motor. This is always the case when the system deviation exceeds a certain value, i.e. if the voltage U4 is larger in magnitude is called the amplitude of the triangular voltage U5. This is usually when starting up of the motor (positive difference) or when braking or positioning the motor from the maximum engine speed with extremely low system friction (negative Difference) be the case. In the first-mentioned case, this involves creating the full, strongly accelerating voltage + Umax and in the second case the application the full, strong braking effect - Umax result.

The fact already mentioned above that when the pulse period TE exceeds a certain limit duration TG, the effect of the holding circuit 39 is put out of operation and thereby the further decreasing voltage U8 can directly reach the subtraction amplifier 28, which increases the Differential voltage and thus a broadening of the impulses applied to the motor Voltage U7 is also shown in FIG. 5, in particular from the waveforms b, c and d within the pulse period TE5. By this measure ensures that the motor does not come to a standstill before reaching the target position comes.

In Fig. 7 is the control characteristic used in the example described together with a positioning process from maximum speed Vmax specified.

The count values 128 to 8 of the counter 25 corresponding to the distance to the target are plotted on the abscissa of the diagram shown in FIG. 7 within the positioning range II. The transformed pulse times * and TE * in milliseconds are plotted on the ordinate. The solid line represents the control characteristic, ie the reference pulse period TFII * within area II. The dashed line represents the actual pulse period TE * for the motor coming at maximum speed from area I. With a maximum motor voltage Umax of 28 Volt and a maximum evaluated difference #Tmax = 5ms results in a gain factor of The measurement limit for the maximum value of the pulse time is = = 5.5 ms. The motor voltage UM is - as already mentioned several times - proportional to the difference between the guide pulse period TF * and the actual pulse period TE * and, as can be seen from FIG. 7, increases in the illustrated positioning range II from 18.5 volts to 0 volts away.

This increases the pulse time of the motor from TE = 1 ms (TE * = 4.5 ms) to (TE) END = 4.5 ms ((per END - 1 ms).

The dash-dotted curve represents the limit curve of the maximum evaluated Difference ATmax of 5 milliseconds max with respect to the curve of the leading pulse period duration TFII *. Along this dash-dotted curve and within the left below This curve would have a motor voltage of + Umax. As from Fig. 7, the dash-dotted curve intersects the abscissa at point 5R. This means that due to the steeply sloping curve of TFII * and due to of the limited measuring range for the pulse period measurement, the maximum possible difference is getting smaller, which means that to the right of the intersection point SR the limit curve for UM = + Umax with the abscissa the maximum possible effective voltage of the motor Umax successively reduced to Umax / 5. Through this gradual decrease in tension Positioning is also possible over short distances without the motor being driven via the Target shoots out.

In FIGS. 8 and 9, the positioning processes are for different line jumps with the supply voltage and the system friction constant values to have.

In these figures, d means transport by one line, c means transport by two lines, b the transport by three lines and a a transport of more than five lines. One line corresponds to a transport of 40 counting pulses of the Way or. Line counter 25. In the upper part of FIG. 8 is in each case the Motor voltage UM occurring during these line switching operations above the covered Distance (counting pulses 128 to 0) plotted. In the lower part of FIG. 8 is in each case the corresponding transport speed also over the distance covered applied. In Fig. 9, however, the transport speed is dependent applied by the time.

A second exemplary embodiment will now be described with reference to FIGS of the inventive positioning control system, which is purely digital is working. In the block diagram shown in FIG. 11, those function blocks are which are shown in FIG. 4 with the partly digital, partly analog working Embodiment match, provided with the same reference numerals.

To the one containing the line counter and the up / down decoder Function block 25 becomes the line 23 for a desired line jump required count value Sc entered. As with the first embodiment 40 counting impulses are entered for a jump of one line at a time, whereby here too the target position is set to the counter reading 5. The motor control circuit 31, which is only shown as a single functional block in FIG. 11, the motor driver stage 35, the function block 36- representing the motor and the load, consisting of the slotted perforated disk and sensor consisting of optical scanning device 37 and the direction identification circuit and function block 40 including the pulse doubling circuit can be used with the corresponding function blocks of FIG. 4 be identical and therefore not described in more detail.

The motor control circuit 31 is dependent on the line 24 of the direction in which the form to reach the newly entered target position must be moved to operate the motor in a forward or reverse direction set.

As a setpoint generator for the desired braking function, this Embodiment uses a read-only memory 50, which, for example, 256, has addressable memory locations of 8 bits each. In the memory addresses A constant value D (see also Fig. 13) is stored in each case from 255 to 128, which determines the normal speed of the transport system. In the memory locations 127 to 0 are the corresponding values for the respective target pulse period time stored for the distance to the target position defined by the address; i.e. the values contained in memory locations 127 to 0 define the desired Braking function. If required, this braking function or braking curve to adapt to certain other system conditions, instead of a Read-only memory (ROM) a programmable read-only memory (PROM) can be used.

The setpoint value A read out in each case from the read-only memory 50 for the pulse period time is sent together with the actual value B to a binary subtraction stage 51 created. This actual value B -the pulse period TE of the clock disk 16 (Fig. 1) sampled clock pulses are obtained by the fact that these from the function block 37 supplied pulses are fed to a pulse period measuring circuit 52, which contains a counter, in each case during the duration of a pulse period TE of an oscillator 53 supplied timing pulses T0 are counted. From later reasons, which will be described in more detail, is in each case at the beginning of a counting period, i. at the beginning of a new clock pulse period TES contained in the time measuring circuit 52 Counter preset to a constant value K, for example to a value of K = 82. The oscillator 53 supplies, for example, a timing signal with a Frequency of 25.6 kHz. The time measurement is therefore carried out with a resolution in 39 microsecond steps.

At the end of a clock pulse period TE, the content of the counter in a buffer register 54 is transferred. During the next pulse period, will the content of this buffer register 54 of said subtracting stage 51 as the actual value B supplied. If the pulse period TE exceeds a certain limit value, for example, the value of 4.4 msec, then the content of the buffer register 54 increased by one unit every 39 microseconds while the pulse period is still running, as a result of the larger difference between the actual and setpoint values the motor current is also increased while the pulse period is still running, so that the engine accelerates again and a premature standstill of the same for example as a result of an undesirable sudden increase in load is avoided, as has already been done has been described in connection with the first embodiment.

The difference d from the actual value B is obtained in the subtraction stage 51 and the nominal value A (d = B - A).

The difference in binary form »is now taken into account of the sign into a proportional motor voltage. this happens preferably again by means of a pulse width modulation of the control deviation obtained representing difference. In this game Ausführungsbei there is the pulse width modulator 55 from a cyclically rotating counter 56 and a digital comparison stage 57, in which the respective content of the counter 56 is compared with the control deviation will. For example, the counter has a capacity of 256 counting steps and counts cyclically with constant counting frequency from this value 256 to the value 0, like this is shown in Fig. 12a by the sawtooth-shaped signal. It is true pointed out that in the ordinate of FIG. 12a, not an amplitude value, but digital count values are plotted, so that the one from the top left falling edges of the sawtooth-shaped signal in reality through digitized counting steps from the value 256 through the value 128 to the value 0 are formed. Because the counter does not count on negative values, but the value 128 represents the axis of symmetry on which the "key ratio" has the value 1: 1, it is for that to be carried out in the digital comparison circuit 57 Comparison required, 'the control deviation also applied to this accordingly to correct, i.e. to increase the value 128.

The subtraction stage 51 therefore does not supply the actual difference A = B - A, but a correspondingly corrected difference β * = B - A + 128. This The facts are also shown in FIG. 12a. Possible values for the corrected Difference d * are shown therein by the step-shaped signal.

The comparison circuit 57 within the pulse width modulator 55 works in such a way that it outputs a high level signal whenever when the corrected difference d * is greater than the count value of the counter 56.

This fact is shown in FIG. 12b. Assigns the corrected Difference d * * values that are above the maximum count of counter 56, i.e. values between, for example, 384 and 256 (this corresponds to an actual Difference 4 from 256 to 128), then the comparison circuit 57 generates a continuous Signal with a high level, as shown in the left third of Fig. 12b.

Such difference values occur, for example, when the motor starts up on when a high speed of rotation due to a relatively great distance from the target is required and therefore a low pulse period is specified as setpoint A and the actual value B is this value not nearly reached yet Has. In this case the motor should be operated with the maximum voltage Umax = + 28 V. will. This portion of the waveform in Fig. 12b with a continuously high level thus causes when the engine is running forwards over the already in connection with the first embodiment described motor control circuit 31 and the motor driver stage 35 applying the maximum motor voltage of + 28 volts to the motor like this can be seen from Fig. 12c. This is the voltage that actually acts on the motor UM (eff) plotted as it is due to the smoothing of the pulse width modulated Motor voltage results. In Figure 12c is the effective motor voltage for the forward run shown; would be the effective motor voltage when the motor is running in reverse have a course that is a mirror image of the signal form in FIG. 12c.

The corrected difference * reaches values that are below the maximum Count value of the counter 56, i.e. are below 256, then the controller arrives in its proportional control range and the comparison circuit 57 gives the value pulse width modulated signals corresponding to the respective difference a *, like this is shown in the middle area of FIG. 12b. Reaches the corrected difference t * has a value of 128 (this case is not shown in FIG. 12a) which is a corresponds to the actual difference of zero, then one obtains a pulse-width modulated. Signal with a duty cycle of 1: 1, resulting in an effective motor voltage leads from 0 volts. With corrected differences a * (t28 the duty cycle becomes less than 1, which leads to an increasingly negative effective motor voltage UM (eff) leads. This negative motor voltage has a braking effect on the motor, as is done to correct it the determined negative control deviation (w = B - A <0) is required.

If the corrected difference t * reaches values less than zero (dies corresponds to an actual difference d (- 128), then the controller leaves the proportional control range and the output from the comparison circuit 57, in The signal shown in FIG. 12b remains at its low level, which leads to that the motor receives the full negative voltage Umax = - 28 volts. This case can occur especially when the engine is running from full speed at low System friction and relatively large moving mass is to be braked. In this case so the negative system deviation can be so large that the correction to the The full braking voltage must be applied to the motor.

As in the first embodiment, the optical Scanning unit 37 supplied, scanned by tracks I and II of the clock disk Clock pulses with the pulse period TE of the direction identification and pulse doubling unit 40 supplied, which via a line 40a a counting direction control signal to the in the counter-decoder unit 25 supplies counter. Over the line 40b, this counter is incremented by means of a pulse repetition frequency that the twice the frequency as the clock signal read from track I of the clock disk. If the motor is running in the specified manner via line 24 to motor control circuit 31 Direction, then the line counter contained in the unit 25 counts down, there the document to be transported approaches the target position. Upon reaching a Count value equal to or less than 8 is a signal to the line 25a Motor control circuit 31 output, which switches off the motor voltage in the driver stage 35 causes. The deceleration of the engine from the at this point existing final speed VE up to speed 0 only takes place through the system friction. The in the counter of the counter-decoder unit 25 by the count value 5 defined target position becomes even with extreme fluctuations in load achieved with an accuracy of + 2 counting units.

The mode of operation is shown again on the basis of the diagram shown in FIG this embodiment of the positioning control system according to the invention explained. In this diagram, on the abscissa from left to right are those indicated by the line counter of the function block 25 defined addresses of the braking function storing Read-only memory 50 (ROM) applied. These addresses correspond to the respective Distance of the recording medium to be transported and positioned from its target position. The target position is also in this exemplary embodiment the count value 5 is set. On the left ordinate is that by the number N of Pulses T0 of the oscillator 53 defined pulse period TE both for the target as well as for the actual value from top (0) to bottom (255) increasing. the The curve labeled A represents the setpoint curve stored in the read-only memory 50 Since the corresponding values in the read-only memory 50 - as already mentioned - stored in the individual memory addresses in the form of 8-digit binary digits.

are, the target value curve A is in reality not a continuous one Curve, but is made through a step-by-step approximation of the corresponding digital values educated. To the left of the ordinate, i.e. in the memory addresses 123 to 256, is in the corresponding memory locations a constant value D (for example with the value 16), which defines the setpoint for the normal speed of the motor.

The setpoint for the pulse period jumps to memory address 127 to a lower value, which can then be used via the other memory addresses up to to memory address 8 of the indicated curve A follows., Because of the at normal speed with a low gain of the control loop, the difference must be a = B - A will be relatively large to the engine necessary for maintaining this Speed to deliver the necessary voltage. Therefore becomes that of the period duration TE counted pulse number N of the pulses T0 of the oscillator 53 adds a constant K, such that the difference between the reference variable and the actual variable is just that motor voltage UM generated, in which in the steady state, depending on the load sets the period TE again. As can be seen from Fig. 13, was in this In the exemplary embodiment, the value K = 82 pulses is determined for this constant. Outgoing of the auxiliary abscissa representing this constant K is on the right in the diagram an auxiliary ordinate is drawn on which the actually occurring values for the period TE are plotted in milliseconds. In the normal speed range In the example shown, counting 14 pulses T0 results in a pulse period of TE = 560 microseconds, which is a transport speed of 38 cm per second. The mentioned constant becomes this number of pulses K = 82 pulses added, resulting in an actual value of 96 pulses. Starting with position 127, i.e. within the positioning range, the actual value has the in Fig. 13 by the curve B, this curve when approaching towards the goal closer and closer to the setpoint curve A, which means that the difference d between the actual value and the setpoint value is getting smaller and smaller, so that the motor voltage is also correspondingly reduced UM decreases. Shortly before the goal, i.e. in the switch-off position, the motor voltage is UM to zero and after switching off the motor voltage, the motor now only runs braked by the system friction up to the target position, which is with a count of is about 5.

The measuring range of the pulse period is TE for the selected Embodiment 6.75 milliseconds, which corresponds to 173 oscillator pulses T0. Together with the value of the constant K = 82 pulses, this results in that in the 8 bits a memory address of the read-only memory 50 maximum storable value of 255 Impulses.

With reference to FIG. 14, which is a highly schematic block diagram illustrates yet another embodiment of the positioning control system according to the invention described. Some function blocks of this embodiment are again with those of the exemplary embodiments shown in FIGS. 4 and 11 are identical. It these are the driver stage 35, which symbolizes the DC motor and the load Function block 36, the slotted disc with the two sensors for the tracks Function block 37 containing I and II as well as the direction of rotation detection and pulse doubling block 40. In this exemplary embodiment, all other functional blocks are replaced by a between the two dashed lines and with the reference number 79 designated microcomputer system and by an integrated counter module 83 realized.

Said microcomputer system 79 is used in many applications of the positioning control system according to the invention is present per se, for example it becomes in the described application of the recording medium positioning in a line printer also for needle selection control for a print in advance and return of the needle print head as well as for various other purposes. By using this microcomputer system 79 which is already present in the device a better utilization of the same can be achieved, so that an extremely economical solution for the system according to the invention results.

The microcomputer system 79 consists of a microprocessor module 80, a read-write memory module 81 (RAM) and a read-only memory module 82 (ROM). These blocks are known per se via data, address and control cable bundle connected to one another. On a more detailed description can therefore be waived. An additional integrated counter module 83 is also connected to the microcomputer system via appropriate conductor bundles, but has in contrast to the latter, only to fulfill functions that are necessary for the control system according to the invention are specific.

This counter module 83 contains three programmable in their mode of operation Counters, the task of which is described below.

Used for commissioning or entering the new target position here too the line 23 labeled Sc.

The function of the counter that stores the distance to the target position 25 is here by a t x 8 bit existing memory location of the read-write memory 81 formed. Such a storage location can of course not be an independent one Carry out the count. The count is therefore carried out by a program routine of the microprocessor Module 80 carried out. Whenever the functional unit 40 in the already described in connection with the other two exemplary embodiments Way a counting pulse is emitted (line 406), this is possibly just in the microprocessor module 80 running program is interrupted and this is transferred from the read-only memory by means of 82 retrieved program data a program routine that, when the engine runs in the desired direction of rotation, a reduction in the memory location mentioned in the read-write memory 81, while when the engine is against moves in the desired direction of rotation, the Content of this memory location is increased by one unit.

The output line 40a of the function block indicating the direction of rotation 40 has an input / output channel contained in the read / write memory module connected to supply this information to the microcomputer system 79.

The comparison between the actual and target value is also made in the microprocessor 80. The values of the reference variable can be stored in the read-only memory 82 in the form of a Be saved in the table. To save storage space, however, it is also possible to to save only a few values and intermediate values by means of a corresponding program routine, e.g. by the above-mentioned one, with the aid of the microprocessor 80. If, for example, the reference variable is to follow curve A shown in FIG. 13, then it is possible to use or also the less curved part of this curve to approximate several straight lines, to store a single value for each straight line and to determine the remaining values using a relatively simple arithmetic function. The values of the reference variable in the more strongly curved part at the end of the curve can be saved individually for better control accuracy.

In principle, however, it is also possible to use the entire curve the reference variable for the individual distances to the target position by means of the microprocessor to calculate.

However, this only makes sense if a mathematically relative simple curve is present, otherwise the necessary for the implementation of the Arithmetic operations require program steps an excessively large memory space would occupy the read-only memory 82 or the one required for the calculation Expenditure of time would be too great.

Of the three counters contained in the counter module 83 are used two for converting the control deviation determined by the microprocessor 80 into a corresponding pulse width modeled Signal that is in the Driver circuit 35 is converted into a corresponding motor voltage. The first these two counters are operated so that during the first half of its counting steps a low potential output and during the second half of its Counting steps an output signal with high potential is generated, i.e. this counter works practically as a rectangle generator. The generated square wave signal has a such frequency or period as this for the frequency of the pulse width modulated Signal is desired.

With the falling edge this generated by the first counter The square-wave signal is sent to the second counter that corresponds to the system deviation Value stored from this counter by one of the microprocessor delivered clock signal is counted down until the value zero. As long as this second counter is on a value other than zero, it emits a signal with a first logic level and when the count value zero is reached for the remainder Duration of the pulse period defined by the first counter with a signal a second logic level, whereby by the ratio of these two signals the duty cycle of the pulse width modulated signal is determined. But there with a control deviation of zero, the effective motor voltage will also be zero should, the duty cycle must be 1: 1 in this case.

For this reason, it becomes the actual one that represents the control deviation Value adds half of the value representing the payment capacity of the second counter and this modified system deviation is always at the beginning of the first Counter defined counting period is loaded into the second counter.

In the event that the actual system deviation is zero, thus a value is loaded into the second counter which is exactly half of its counting capacity amounts to. Positive values of the control deviation lead accordingly to a pulse duty factor greater than 1, negative values of the system deviation to a pulse duty factor of less as 1.

The third counter of this counter module 83 is used for pulse time measurement, i.e. to determine the actual value of the pulse period. Every second from the function block 40 via the line 40b to the microprocessor module 80 delivered clock pulse is said third counter to its full counting capacity charged and by the clock signal emitted by the microprocessor until the occurrence of the next but one clock pulse emitted by function block 40 is counted down count value contained in the third counter at the end of such a pulse period corresponds to the modified actual value of the pulse period TE * as it is in context with Fig. 3 has already been described. This modified actual value is, as already mentioned, in the microprocessor module 80 with the one taken from the read-only memory 82 or the calculated target value of the pulse period and the received Gel deviation is used in the manner already described to form the pulse width modulated Motor signal used.

L e r s e i t e

Claims (18)

POSITIONING CONTROL SYSTEM FOR A DC MOTOR DRIVEN TRANSPORTMECHAN ISMtJS Patent Claims: 3 Positioning control system for a DC motor driven transport mechanism, in particular for recording media, with one-with the motor shaft coupled pulse generator, one the distance from the target position storing counter and a speed controller for the DC motor, its setpoint generator a reference variable dependent on the current status of the meter delivered characterized that the pulses supplied by the pulse generator (16, 17) of a timing circuit (38,39; 52,53,54) are supplied to one of the respective period durations (TE) of these Pulses corresponding actual value (U9; B) to generate that the reference variable (U2; A) one of the respective target period duration. (TF) is the appropriate size and that the Control deviation obtained by calculating the difference between the reference variable and the actual value (U.3, U4; d *) controls the generation of the voltage (UM) effective at the direct current motor (15). 2. Positioning control system according to claim 1, characterized in that that the setpoint generator (26, 27; 50) for the by the respective counter reading of the counter (25) marked distance to the target position output reference variable (U2; A) follows a function which for a given motor and load characteristic an approximately linear reduction of the motor voltage down to the value zero im Target area (III) allows. 3. Positioning control system according to claim 2, characterized in that that the motor (1.5) when it reaches a certain value of the counter (25) defined target area switched off or short-circuited and from the to this Point in time due to the final speed (VE) present due to the pulse time control the system friction is braked to a standstill. 4. Positioning control system according to claim 1, characterized in that that the control deviation (U.3, U4, j *) controls a pulse width modulator (30; 55), its output signal (U.6) optionally via a motor control circuit (31) a Motor driver stage (35) is supplied. 5. Positioning control system according to claims 1 to 4, characterized characterized in that the setpoint generator (26s 27) consists of a digital-to-analog converter (26) for converting the count value of the counter (25) into a proportional voltage (U1) and a function generator (27) which is dependent on the one proportional to the count value Voltage (U.1) one of the named predetermined function corresponding voltage (U2) generated that the timing circuit (3,8, 39) from a pulse duration voltage converter (38) for generating an inside each pulse period (TE) starting from a fixed voltage (U8max) proportional to time falling voltage (U8) and a voltage holding circuit (3.9), which the value of the falling voltage (U.8) at the end of a pulse period (e.g. TE3) for keeps the duration of the next pulse period (e.g. TE4) constant (Ug). 6. Positioning control system according to claim 5, characterized in that that the value representing the actual value is constant for the duration of one pulse period (TE) maintained voltage (Ug) and the voltage (U.2) representing the reference variable a subtraction amplifier (28) to which a voltage amplifier (29) to generate an amplified differential voltage representing the system deviation (U4) is connected downstream. 7. Positioning control system according to claims 4 to 6j thereby characterized in that in the pulse width modulator (30) the applied thereto amplified differential voltage (U4) by means of a sawtooth or triangular voltage (U5) in a manner known per se into corresponding width-modulated voltage pulses (U6) is converted. 8. Positioning control system according to claims 4 to 7, characterized characterized in that when the pulse duration voltage converter (38) has a certain Detects the pulse period (e.g. TE5) r exceeding the limit period (? G), this the function of the voltage holding circuit (39) is out of operation and the time proportional the falling voltage (U8) is applied directly to the subtraction amplifier (28). 9. Positioning control system according to claim 5, characterized in that that the function generator (27) is an operational amplifier with negative feedback by means of a diode is. 10. Positioning control system according to claims 1 to 4, characterized characterized in that the setpoint generator has a read-only memory (50) with at least one corresponding to the number of steps of the counter (25) defining the positioning range Number of memory addresses is in which the desired predetermined function Representative values (A) are stored in binary form and 'by the respective count values of the counter (25) can be called up that the time measuring circuit (52, 53, 54) consists of one Oscillator (53), one by the output pulses of this oscillator each for a period of the pulses generated by the pulse generator (16, 17) can be incremented Counter (52) and a buffer register (54), which at the end of a period (TE) takes over the counter value and this as the actual value for the next pulse period (B) provides. 11. Positioning control system according to claim 10, characterized in that that in a binary subtraction stage (51) the difference (6) from the read-only memory (50) retrieved binary value (A) and the content of the Buffer register is formed. 12. Positioning control system according to claims 4 and 11, characterized characterized in that the pulse width modulator (55) consists of a periodically rotating Counter (56) and a comparison stage (57), which depends on a greater-less comparison between the one formed by the subtraction stage, representing the control deviation and, if necessary, by adding the counter mean value modified difference (t *) and the periodically changing count of said Counter (56) emits a pulse-width-modulated signal whose pulse repetition frequency on the cycle frequency of the counter (56) and its pulse width by the respective elapses until the counter value corresponding to the amount of the control deviation is reached Time is determined. 13. Positioning control system according to claims 10 to 12, characterized characterized in that when the counter (52). the timing circuit a predetermined, a certain limit period (TG) defining count value exceeds the Contents of the buffer register (54) during the still running pulse period by the Output pulses of the oscillator (53) is increased. 14. Positioning control system according to claims 1 to 4 using a microcomputer system consisting of a microprocessor module, a read-write memory module and, a read-only memory module, characterized in that the distance Counters storing the target position through a memory location in the read-write memory module (RAM, .81) is formed, the content of which in each case when one of the pulse generator (1.6, 17) to the Microprocessor (80) delivered pulse as a function of the direction of rotation of the motor (15) with the help of an in the read-only memory (ROM, 82) stored program routine is decreased or increased by one unit. 15. Positioning control system according to claim 14, characterized in that that the pulse period values of the reference variable are partially stored in the read-only memory (ROM, 82) are stored un on the other hand using a likewise calculated in this stored program routine by the microprocessor module (80) will. 16. Positioning control system according to at least one of the claims 14 and 15, characterized in that a counter module is attached to the microcomputer system (83) includes the three operationally programmable counters contains, of which the first when each occurs from the pulse generator (1.6, 17) delivered pulse is loaded to the full count value and then by a clock signal supplied by the microprocessor (8.0) until the next pulse occurs is switched downwards, after which the reached, the actual pulse period count value representing the microprocessor (80) to form a value representing the control deviation Word is fed. 17 .. Positioning control system according to claim 16, characterized in that that of the other two counters of the counter module (8.3) the one to generate a square wave signal with one of the desired frequency for the pulse width modulated Motor signal operated according to frequency will, while in the other counter at the beginning of each period of said square-wave signal a value corresponding to the control deviation, which if necessary, by adding of the counter mean value of this counter is increased, is entered and this counter then post-abwirts by the said clock signal supplied by the microprocessor (80) is switched, this counter sending a signal until the count value zero is reached with a first level and for the remainder of the period of said square wave signal supplies a signal at a second level to the motor driver stage (35). 18. Positioning control system according to one of the preceding claims, characterized in that the driver stage (35i has two electronic switches (T1, T2), of which one (T1) is modulated by the positive amplitudes of the pulse width Motor control signal (U6) for applying a positive voltage (+ Umax) and the other (T2) through the negative amplitudes of said control signal for applying a negative one Voltage (-Umax) switched through to the motor winding smoothing these voltage pulses will.