DE2310443C3 - Procedure for position control of speed or armature voltage controlled DC drives - Google Patents

Description

The variable formed as an additional current setpoint intervenes correctively in the current control, with (1 - Is) -K is limited to the value ± I and K an adjustable gain factor and the value 1 or ± 1 equals 100% of the valid control signal level mean.

2. The method according to claim I. characterized in that until the beginning of the braking phase a constant corresponding to the maximum permissible speed or armature voltage setpoint Quantity that is synonymous with 100% of the valid control signal level, as speed or Anchor voltage setpoint is specified.

3. The method according to claim I. characterized in that that up to the beginning of the braking phase the speed or armature voltage setpoint is derived from the distance (I.s) still to be covered will.

4. The method according to claim 1, modified in that the additional current setpoint after the relationship

i \. = | I Is-H -) - (I - Is) - K Li-eregelunaen in industrial plants should generally be time-optimal, ie. it is not enough. To approach the more "wished position with the smallest possible u iT.yuHssieen error, but this should be done generating regime time STder k. This is true nbesonderemMaßefürdieWalzenanstellung.n rolling mills as the drive is usually a stromriduergespeister. Separately excited DC motor

is formed and switched to the current setpoint (I _x ) with a sign.

5. The method according to claim I, characterized in that that the target word for the addition (i.s.) corrected Stromsollwerl is limited to a value that corresponds to the maximum permissible Stromsollwcri is equivalent to.

The invention relates to a method for regulating the position of speed or armature voltage regulated DC drives with subordinate current control.

Known position controls are generally based on the principle of the so-called Stromtatver ahrens ^ f »Built (AEG-Mitteilungen 54 [1964] 111- p. O78 to 681). The difference between the nominal position and the * power width is fed to a position controller. the Laaereafer forms depending on the existing Web error the speed setpoint and the speed controller the current setpoint depending on the existing speed error. So there are three there are subordinate control loops in each case. The current controller then influences, for example a pulse device that generates the ignition pulses for the Converter supplies. With analog methods of measurement the situation. z. B. by means of a potentiometer or resolver the difference between the nominal position value and the sea value is calculated. so the path difference Is directly from Formed skis. Be, digital process can be in e, nf , eisten, case the path difference by a subtract are formed. Depending on the task at hand, there is also a computer or a process computer for use.

When the position control is switched on, i.e. at the point in time from which the drive deviates from the current one Position in the new, given position is the position controller and the speed controller overridden, and only the current controller, is leading, This means that it leads the armature current to the current limit permissible for the motor. This is in the interests of the maximum possible acceleration necessary Does the engine have its maximum speed after starting up , reached so the speed controller is flour; more overdriven-This the setpoint for the current controller is ο reduced so that the motor only supplies the current leads which is necessary for overcoming the friction while maintaining the speed. -, s, Ite Difference between the target and actual position so If the braking of the drive has become small, the position controller also goes out of the overriding range out. The speed setpoint is then brought to zero by the position controller so that the ο Drive with the specified accuracy in the comes to the right position.

In the known method is the reinforcement determined in the position control loop by the ratio of the maximum speed to the braking distance. This in turn determines the gain of the speed controller. The greater the braking distance and the shorter so that the gain in the position control loop, st. the greater the gain of the speed controller must be so that this even with very small paths Is reacts to the correspondingly small speed setpoints in such a way that the output from it * Current setpoint is sufficient to control the drive Procedure in the Sollage required ^ minimum current to feed. The reinforcement ues ^ rcnza,., Reg, er: cannot be increased indefinitely, but is limited by the mechanical part of the drive, its elastic parts and coupling slack at over A certain gain is not reached

55

h0

stir permissive vibrations.

If the position control is based on a digital principle, additional difficulties arise. The path Is still to be traveled must be converted into an analog voltage IbZ ^- W. Strom) by a diiiital-analog converter. Since the digital value changes in stages, this also happens with the analog voltage. The analog speed setpoint does not ■ change continuously during the braking phase. Rather, the speed setpoint is composed of a direct voltage component and an alternating voltage component. In the case of a high control quality, in which a large gain of the speed controller is required, this is already overridden by the alternating voltage component, whereby the gain is reduced. As a result, there is a delayed use and before a reduction in the braking current and thus in turn the necessity. to bring the braking point forward even further. As a result, neither an optimal time response nor the required accuracy is achieved.

The object of the invention is to raise a method " which avoids the disadvantages of the known method, and thus a cheaper dynamic one Behavior and a higher accuracy, especially with longer braking distances.

According to the invention, this object is achieved in that the difference is continuously formed from two variables, of which the first is derived from the Wes> Is of the drive that has to be covered up to the specified target position and the second is derived from the square of the current drive speed ir The polarity of this difference is reversed, ie when the relationship Is' - / r> 0 changes into l _s ' _ if < 0, where Is' is a variable derived from the variable Is through amplification and limitation to the valid control signal level, which results in the braking phase of the drive it is initiated that the speed or armature voltage setpoint specified for the drive for acceleration and, if necessary, subsequent travel at constant speed is switched to zero and that during the braking phase one of the distance Is still to be covered and the square of the current drive speed; j ^j after the relationship is The distance covered during the braking time

This relationship can also be written

2- I-

If equation (2) becomes equation (1) you get

used so

2 · In

or reshaped

I.ν =

GD ¹ ■ η

375 · Λ /

GD ² ■ η ²

2 ■ 375 ■ Λ /

j = (.1.VH ²

- Ks) K If all constants are combined to k , one obtains

and with k =

lv = k-ir

1 .s- = η-.

(3)

The relationship In = A: - / r _: corresponds to the known basic form of the braking parabola .s = r ² with the distance still to be covered to the stopping point .s and the respective speed r. In the form r = | '.v, the braking parabola is also used in a device known from DT-AS 15 88 074 for braking a machine, by immediately before stopping, shortly before the desired stop point, the respective speed with the square root of The remaining distance to be covered up to the stop point is compared and a variable for controlling a mechanical braking device is derived from the difference between the two.

Based on the relationship (3), there are now various options for obtaining the additional current setpoint. So this relationship can be interpreted in two ways:

l.v

The variable formed as an additional current setpoint intervenes correctively in the current control, where (1 - Ix) · K on the value ± 1 is limited and K is an adjustable gain factor and the value 1 or ± 1 is the same Means 100% of the valid control signal level.

When generating the additional current setpoint, the invention is based on the following consideration:

GD ² η
'"= 375-A / · ⁽¹⁾

Herein means

GD ¹ = moment of inertia in kpm ² ,

Il IVlULUIUIVIIIAllll l- ». ·« -N- ^ iliil Sjw LJ Ϊ <- I 1 «Γ. Ιί ι ι

in rpm.
M = engine torque + frictional torque

in kpm,
ι, - braking time in s.

I .s- - η- = 0.

In principle, both forms can be implemented. The first relationship (4) is during the braking phase continuously the quotient aur. Is and / r formed and compared with the value 1. The value 1 means here

As is common in control engineering, 100% of the valid control signal level. The right-hand side of the equation is only zero if Is and ir decrease to the same extent during the braking phase. For example, if the drive does not brake fast enough, Is will assume smaller values faster! - !, while; r decreases Uinusy.mer. So then is

Ls becomes ζ. B. get a negative voltage.
On the other hand, if the drive brakes too hard, you get with it

; r

/ .. B. a positive voltage.

These voltages can be applied to the current controller as additional current setpoints. The scarf κι

technical realization of the relationship -j = I

assumes, however, the use of dividers that still provide sufficiently accurate values ^{for In- 1} O and h ^{2 - * ().} i ->

In the second relationship (5), the same result is immediately obtained. It should be noted, however, that the gain in the position control loop decreases with decreasing In. But so that the position control is sufficiently accurate. the gain must remain approximately constant over the entire range. This can be achieved to a certain extent by adding an amplifier with a limited output. However, because it is more precise, it is better to multiply the voltage 2i obtained on the basis of relation (5) by a factor which becomes greater as In becomes smaller. If one chooses for this, for example, the factor A ₁ = _{) s} ; . ^{the voltage! 0} is obtained as the additional current solvert

Ma η then receives the voltage as an additional romsoll value

V _x =

I N - »Γ

In

(6)

The circuitry implementation of relationship (6) also implies the use of amplifiers here with high accuracy.

The possibility according to the invention of obtaining the additional _{current setpoint is obtained if the relationship (5) is multiplied by the factor A 2} = (1 - In), the value 1 in turn signifying 100% of the valid control signal level. So that the gain in the position control loop remains approximately constant during the major part of the braking distance, the resulting parabola must be subsequently amplified by multiplication with a constant factor K and limited to the value il (= 100% of the valid control signal level). The voltage is then obtained as an additional current solvert

V ₁ - I Ix - / rl - II - Is) ■ K. (7)

The formation of the additional current setpoint according to the relationship (71 has the advantage that the gain in the position control loop only decreases when Is has become sufficiently small, so that the drive is correctly brought into the set position and the braking current is finally reduced This is advantageous because the rate of change of the armature current ί J ₁ J may never be arbitrarily large with regard to the drive motor.

With very high demands on the accuracy of the Laueregeluni; can improve the process according to the invention! become, because the after the The stress obtained in relation (7) is extracted.

L ', = | (In - H ² ) (l - In) - K.

The drop in the additional flow rate for In M) is then steeper, which increases the accuracy of the position control.

The invention is described in the following Bc notation explained in more detail with reference to an embodiment shown in the drawing, at the same time further inventive features serving the embodiment of the invention are shown. It shows

F i n. I the course of the quantities - -. In - ir and

l.s

as a function of I ν for the limiting case tr = 0.

I s - ir

F i g. 2 shows the course of the quantities In - ir. (I ν - / r) · (1 - I s). (I .s- - η ² ) · (I - Ls) -K

Ls - H ² ) - (l - In) - K

as a function of I ν for the limit case / r = 0.

F i g. 3 the control-technical structure diagram of a position control according to the invention.

The F i g. 1 and 2 show a standardized representation

the course of the sizes 1, Ls - / round ^ls ~ "or I .s I .s

IN - H ² , (. IS - H ² ) · (1 -. IN), (IN - ΙΓ) ■ (1 - IN) ' K

and In - η ² ) - (I - In) - K as a function of the dated

Drive to the target position, distance still to be covered In. The values were plotted for the borderline case h ² = 0 and for Is from 1 to 0. Here, the distance from 1 to 0 corresponds to the braking distance on the abscissa, where Is = I denotes the braking point and Is = 0 denotes the target position to be retracted. Ir F i g. 1 were only used for the sake of the draftsman! see representation for the ordinate, two different scales used. In Fig. 2 was selected for the adjustable gain factor K = IO and the magnitudes amplified in this way were limited to the value 1, ie to 100% of the valid control signal level.

In Fig. 3 is used as a drive to move to a given location, position or position an external excited DC motor M. A Tachometerma machine T supplies the actual speed value η and a distance measuring device S an actual position value corresponding to the distance traveled by the drive. The ii of an addition point 2 from the predetermined position soliwert s _s and the actual position value ν formed path difference In is amplified in an amplifier 3 and limited to the control signal level. With the adjustable gain of the amplifier 3, the position of the braking application point is determined depending on the conditions of the respective system. In this case, the gain is expediently selected so that the drive comes to a standstill a little too early with the maximum permissible braking current, because this braking current is reduced by the additional current setpoint, but not increased with regard to the permissible current values may. Di the addition points 4. 5 and another Vei

stronger 7 applied initial tension I \ has above a Wcgdifferen /!. its constant maximum determined by the amplification in the amplifier 3 Worth. If this value becomes a speed controller shown here as a PI controller via a switch 15 switched on as maximum rotation setpoint, then the motor current increases so quickly. as is the case with the dimensioning of the converter system and is permissible with regard to the mechanical and electrical design of the drive. the The drive then accelerates correspondingly quickly. If a very small path is now specified for the position control, so the motor current can because of the necessary for the control or reversal of a converter finite time cannot be switched to braking mode as quickly as it is for a stable one Entry into the target position would be required. Rather, the drive would overshoot. To such a swing To prevent this, when traversing very short distances, only a reduced setpoint may be applied to the Speed controller8 can be switched. Amplifier 7 is used for this purpose. With the appropriate setting the gain and limitation of the amplifier 7 is achieved that down to a smallest Path. at which the drive does not yet overshoot, the full speed setpoint, on the other hand for even smaller ones The distances to be traveled are only given a correspondingly reduced speed setpoint.

The actual speed value provided by the Tachometermasehinc η T is applied to the input of a function generator 6, the output a the square of the input speed zufuhrt ir voltage proportional to the summing point. 5 The difference formed in addition point 5! Ix '- ir) is fed to a trigger 9 and the first input of a multiplier 10, at the second input of which a difference (1 - Ix' (formed in the addition position 4) is given. The value 1 means, as already mentioned. 100% of the It can be fed to the addition point 4, for example, in the form of a constant DC voltage, the amount of which corresponds to the control signal level.

The output of the multiplier 10 supplies a voltage proportional to the product Ux '-; r) ■ Π - Ix'), which is amplified by a factor of K in an amplifier with adjustable gain and adjustable limitation, limited to the control signal level, and in a function generator 12 is rooted. The functional encoder 12 thus supplies one of the size

I Ix

corresponding voltage, which is switched as /.usalzstromollwert / _s via a switch 13indcraddition point 14 controlled by the 1 _{rigger 9 to the current setpoint I x} supplied by the speed controller 8 with the correct sign.

If the drive is now to be moved into a new target position, the shearers 13 and 15, which can be designed, for example, as relays or field-effect transistors, are left at the start-up time, in which FIG. 3 switching position shown. While the switch 13 is still open κι. lies at the finger of the speed controller 8 the difference formed in an addition point 16 between the speed value n _s supplied from the output of the amplifier 7 via the closed switch 15 and the actual speed value supplied by the tachometer machine T ». From the control deviation, the speed controller 8 forms a current setpoint value i _iS - for the subordinate current control loop. The current setpoint value / _x is fed to an addition point 18 via a limiting element 17, the function of which will be explained below, and there compared with the current actual value / '. In the event of a setpoint / actual deviation, a current regulator 19, shown as a PI regulator, then influences a pulse device 20, which supplies the ignition pulses for a reversing converter 21 which feeds the drive motor.

If one disregards the already mentioned case of the procedure of very small ways. the speed controller 8 is thus acted upon with the maximum permissible speed setpoint (= 100% speed setpoint) from the starting time. The drive is therefore accelerated as quickly as the electrical and mechanical dimensions of the drive allow. It is initially Ix and therefore Ix 'is greater than IR. The further the drive is moved into the predetermined desired position, the smaller Ix is and the larger ir. In so-called trapezoidal drive movement ir is however greater only during the acceleration phase and remains Reaching the maximum drive speed constant. In both cases, the braking application point is given when Ix is less than ir . This is the case when the output voltage Ix 'of the amplifier 3 is out of limit. The difference Ix '- ir formed in the addition point 5 then reverses its polarity. This polarity reversal switches the trigger 9, which simultaneously initiates the braking phase of the drive by setting the speed setpoint ιι _χ for the speed controller 8 to zero by switching the switch 15 and, on the other hand, switching on the correction value for the current setpoint by closing the switch 13 . The trigger 9 is designed in such a way that it does not tilt back after switching once, even if Ix '> ir should later become Ix'> ir. Only when the position error is zero is it tilted back again by switching off the position control. At the moment of switching on, the current correction value is zero. The drive will therefore initially carry the maximum braking current. Depending on the deviation from the set braking parameter and thus according to the amount of the additional current setpoint _{i s applied to the current setpoint \\ crt ί χ} at the addition point 14, the brake current is more or less reduced during the braking phase until the drive stops in the specified target position 17 is provided for security reasons, because the Zusatzstromsollwerl i _x with deir coming from the speed controller8 current setpoint ι, together can form a sum that in unfavorable fill, z. B. when adjusting the drive, is greater than the maximum permissible current setpoint. The sudden specification of the speed setpoint NuI at the beginning of the braking phase has the advantage that the converter is switched to alternating mode as quickly as possible.

The example shows the application de eiiindungsgemaßcn method for position control of a rotationally controlled direct current drive. It lets fall with the same success with only minor changes also for position control of armature voltage control (Use direct current drives is that the addition point 16 instead of de

Actual speed value / ι the armature voltage actual value L _{1 of} the direct current motor is supplied and the output voltage of the amplifier 7 is now the armature voltage setpoint value L '. _ls represents. The regulator 8 thus becomes an armature voltage regulator. >

For this purpose 2 sheets of drawings

Claims (1)

Patent claims:: o 1. Procedure for position control of. Number or armature voltage controlled track current drives with superimposed current control, thereby characterized in that the difference is continuously formed from two quantities, from which the first of the distance to be covered up to the specified target position (Is) of the drive and the second derived from the square of the current drive speed lir) are that with reversal of polarity this difference, i. H. in the transition of the relationship i.s '- ir> 0 in Is' - ir <0, where Is' one of the size I.s through amplification and limitation represents the quantity derived from the valid control signal level, thereby the braking phase of the drive is initiated that the drive for acceleration and possibly subsequent Travel at constant speed, set speed or armature voltage setpoint to zero is switched and that during the braking phase one of the distance still to be covered (I.s) and the square of the instantaneous drive speed (ir) according to the relation / _s _ = (.Ix-Ir) - (I - Is) - K