Note: Descriptions are shown in the official language in which they were submitted.
CA 02240106 1998-06-09
Description:
Method and device for the regulation of a drive
5 The invention concerns a method and a device for the regulation of a drive for jerk-free
starting, for example for a lift, a crane or a vehicle.
A drive device, which is to make a finely meterable and jerk-free starting behaviour
possible, has become known from US 4 995 478. The regulation of the drive takes place
10 on the basis of data which are supplied on the one hand by a load-measuring device
arranged at a lift cage and on the other hand by a speed sensor which measures the
rotational speed of the drive motor and converts it proportionally into a speed. In order to
ensure jerk-free starting in upward direction or in downward direction, the friction values
are also to be compensated for in that case.
In the case of the afore-mentioned drive equipment, the load in the cage must bemeasured with the aid of a load-measuring device arranged at the lift cage in order to be
included in the regulation process. The exact load values necessary for the regulation
require a generally cost-intensive load-measuring device which must be mounted and
20 wired at the lift cage with a relatively large amount of work.
The invention is based on the object of proposing a method and a device for the regulation
of a drive of the initially mentioned kind, which do not have the afore-mentioned
disadvantages and enable jerk-free starting in a mode and manner favourable in cost.
This object is met by the invention characterised in patent claim 1.
The advantages achieved by the invention are to be seen subslanlially in that, apart from
an exisbng drive regulation provided with regulation of rotational speed and torque, a
30 superimposed rapid rotational speed regulation, which can be realised with minimum
technical effort, is provided for the holding of the load after opening of the holding brake.
Advantageous developments of and improvements in the method and the device, which
are indicated in claim 1, for the regulation of a drive are possible by the measures
35 mentioned in the subclaims. The load in the lift cage can be measured by a further
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processing of the target torque value and the actual rotational speed value, whereby the
drive can be so regulated with little material effort that jerk-free starting is made possible.
Thereby, appreciable cost savings result, since no additional hardware, such as load-
measuring devices, is needed at the cage. Beyond that, the lift cage construction is
5 simplified and expensive rebuilding of the cages in the case of modemisations of lift
installations becomes superfluous.
An example of embodiment of the invention is illustrated in the drawing and more closely
explained in the following. There:
Fig. 1 shows a block schematic diagram of an existing drive regulation, a
superimposed rapid rotational speed regulation and the computation of the
load in a lift cage,
Fig. 2 shows signal courses of the starting behaviour without load measurement,
Fig. 3 shows signal courses of the starting behaviour with load measurement and
Fig. 4 shows signal courses during the measuring of the load.
Fig. 1 shows an overall block schematic diagram by way of example at a lift installation
with an existing drive regulation 1, a superimposed rapid rotational speed regulation 2 and
a processing unit 3, which are responsible for the computation of the load in a lift cage 5
with the aid of a target torque value and an actual rotational speed value. Furthermore
25 schematically illustrated are a drive motor 6, a drive pulley 7, a counterweight 8 as well as
a speed limiter cable 9, which runs over deflecting rollers 10 and is fastened at the lift cage
5. The methods for holding the load and for computation of the load in the lift cage 5 are
described more closely in the following by the example of this lift.
30 An actual rotational speed value V,st, which is measured by means of a tachometer DT1,
for example a digital tachometer, at the drive motor 6 and an actual movement value S,st,
which is likewise measured by means of a tachometer DT2 on the basis of the movement
of the speed limiter cable 9 of the lift cage 5, are fed to the existing drive regulation 1, from
which a brget torque value TMSOLL is ascertained by means of target travel values REF
35 and a target drive torque value TMSOL10 resulting from a first regulator S-REG and a
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second regulator V-REG. The target torque value TMSOLL and an actual current value ljSt
are fed to a subordinate torque regulation 12 and finally conducted to an inverter UR for
the drive motor 6.
5 The proposed method according to the invention uses the movement of the tachometer
DT1 at the drive motor 6 after the opening of the holding brake for the detection of a
torque at the brake.
In principle, the drive motor 6 is regulated to the target rotational speed value zero by
10 means of the rapid rotational speed regulation 2 before the target value REF for the travel
starts. During a time TSW (for example less than 0.1 seconds), a holding moment
corresponding with a target torque value TMSOL1 is built up and regulated out to a
stabonary final value.
15 A rapid detection and processing in the 1 millisecond cycle of an actual rotational speed
value Vjst is taken over by a digital regulator 20, wherein the immediate delivery of the
target torque value TMSOL1 resulting therefrom takes place to the subordinate torque
regulation 12 or current regulation in the case of DC drives. This rapid rotational speed
regulation 2 runs for a time TSW parallelly with the existing drive regulation 1, which is in
20 operation during the travel of the lift cage 5 and operates in the 10 millisecond cycle. As
alternali~/e~ in the case of sufficient computing power of the processor, a rapid regulator
with switching-over of the regulator parameters can be used for both tasks. After lapse of
the bme TSW, the output signal TMSOL1 of this regulation is kept at the last state and the
target bravel value REF is started.
In order that the ,olational speed regulation 2 rapidly reacts to an actual rolational speed
value Vjst unequal to zero, the regulator 20 operates with high initial amplification at the
limit of stability. This amplificabon can be chosen to be higher by a multiple than for the
existing drive regulation 1, because the scanning time (1 millisecond instead of 10
30 milliseconds) is shorter and because only the directly coupled rotating mass of the drive
motor 6 with the drive pulley 7 is decisive for the stability of the regulation in the case of
the extremely rapid regulating process.
In the case of the very rapid movements of the drive pulley 7, which last only a few
35 milliseconds, the elastir~lly coupled and weakly damped masses of the lift cage 5 and the
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counterweight 8 remain virtually at rest. This also means that the compensating
movements of the drive pulley 7 are hardly noticeable in the lift cage 5.
In order to avoid disturbing reactions on the lift cage 5, which are caused by the regulating
5 oscillations, and an overload of the power-setting member, the amplification of the
regulator 20 is reduced by a certain amount from a high initial value for each 1-millisecond
time interval so that the regulating oscillation decays to zero after a preset time has
elapsed. The lower limit value of the amplification is so chosen that the regulating loop
displays aperiodically stable behaviour.
For a smaller imbalance, i.e. in the case of partial load in the lift cage 5, the possibility
exists that the rotational speed signal interrogated in the 1 millisecond cycle detects no
movement in the drive pulley 7 in consequence of the low amplitude resolution. If the
actual rotational speed value Vjst remains zero during a settable time after freeing of the
15 regulation, a flag "imbalance small" is set. This flag has the effect that the regulation
processes only the rotational speed signal from the 10 millisecond cycle with higher
amplitude resolution.
In addition, a target value TMKOR is superimposed on the torque regulation as soon as
20 one of the two rotational speed signals indicates a movement of the drive pulley 7. The
direction of the target value is so chosen that a torque against the direction of movement is
built up. The amount should be such that about 50% of the maximally required holding
torque is produced.
25 In order to make certain that the rapid regulation process conbrolled in part by way of fixed
time sequences is not already started by interference signals in the actual rotational speed
value Vjst, a response threshold is provided. The afore-described regulating process is
initiated only when the absolute value of the actual rotational speed value signal Vjst
exceeds the preset U ,reshold value and the com"~and for the opening of the holding brake
30 is present.
The process for the computabon of the load in the lift cage 5 by means of the processing
unit 3 is described more exactly in the following. In order to control a group of lifts
efficiently, knowledge of the load state of each individual lift cage 5 is necessary. In
35 particular, the states "empty", "full" and "overload", the latter also due to regulations, must
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be able to be detected relatively accurately. In order to achieve this object, certain
boundary conditions must be fulfilled on application of the method described in the
following. These comprise:
5 - not too high a friction and
- the static friction may not be significantly greater than the sliding friction.
Lifts without gears and lifts with gears without self-locking are particularly suitable for this
method.
A mean value TMMIT is formed by addition of the target torque values TMSOLL for each
scanning cycle over a certain time interval, which corresponds approximately with the
transient time to a stable end value, and by mulliplicalion with a conslanl K1. This mean
value is in tum converted by mulLiplicaLion with a second constant K2 into a load
15 measurement value TMMlTkg in kilograms. The constant factor K2 contains the
conversion of the torque at the drive motor 6 to an equivalent load in the lift cage 5, i.e. the
l.dns,l,ission ratio of a possibly present gear and/or a cable looping, the radius of the drive
pulley 7 and the gravitational constant are contained therein. Beyond that, all influencing
magnitudes, which apart from the useful load in the lift cage 5 produce a torque at the
20 drive motor 6, are comprehended by the magnitude UNBAL. These are:
- the counterweight 8,
- the weight of carrying cables 25 not fully cG",pensated for by compensating elements
and
25 - the hanging cable.
The last two influencing magnitudes are dependent on the posilion of the lift cage 5 in the
shaft. The position on the shaft is, however, known to the lift control and the
co"esponding values can thus be computed.
The load measurement value TMMlTkg computed above contains a portion of the friction
in the system, which falsifies the results accGrd;ng to direction of movement during the
rapid regulation process. If, however, an osci"ation with change of direcbon and decaying
amplitude occurs (as described initially for the rapid rotational speed regulation 2) and the
35 mean value formation takes place only over a time interval which corresponds with the
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duration of the oscillations, the mean value of the frictional component is approximately
equal to zero. Measurement errors, which result due to friction at the drive motor 6, gears
and drive pulley 7, are to a large extent eliminated thereby. The decaying oscillation is
thus a significant element of this load-measuring method.
According to the state of load of the lift cage 5 and the position in the shaft, the oscillation
process as described above can be influenced in consequence of reaction of the cable
forces on the drive pulley 7. In the extreme case, this undesired oscillation does not come
about at all. In order in these cases to detect the component due to friction in the formed
10 measurement value described above, a tachometer signal IVT10 as well as the absolute
value of the tachometer signal IVT10 are integrated. There is thus obtained the two values
IVTS and ABSIVTS as well as the quotient IVTQ = IVTS/ABSIVTS. The value IVTQ is a
factor which is multiplied by the measured frictional force referred to the circumference of
the drive pulley 7 and the factors of looping and gravitational constant K3. This result is
15 added to the load measurement value TMMlTkg subject to consideration of the polarity.
From these values, the load in the lift cage 5 in kilograms results finally.
The measurement of the friction as well as of the position-dependent imbalance takes
place by a leaming travel up/down over the entire lifting height during the commissioning
20 of the lift installation.
Figs. 2 and 3 show signal courses of the starting behaviour with and without processing
unit 3 for computation of the load. The motor torque TMH, acceleration in the lift cage AK
and speed of the lift cage VK are indicated. Evident in particular is the smoother starting
25 behaviour with inclusion of the processing unit 3 with the aid of the significantly smaller
acceleration peaks and the more rapid transient process.
Fig. 4 furthermore shows signal courses of the processing unit 3 for computation of the
load from the target torque value TMSOLL and the tachometer signal IVT10 and the30 associated resulting courses of the target value TMS as well as the integrated tachometer
signal IVTS.
