Elevator drive control apparatus for smooth start-up

An elevator control apparatus suppresses the jerk at the start-up of speed controlled elevator installations in both directions of travel, not only the friction jerk at the transition from the static friction to the sliding friction, but also the imbalance jerk at unbalanced car loads. A set point signal multiplier is connected to the output side of a set point memory in the hoist motor drive control and the set point multiplying factor can be controlled by way of an on/off circuit. The multiplier is switched, prior to the start of the movement, by the on/off circuit to a value greater than one, and is switched back to one at start of movement in the direction of travel. The motor driving force is controlled to a value which, when summed with the imbalance force, is equal to the sliding friction force at start-up. This suppression of jerks is eminently suitable for the refitting of controlled elevator drives and increases, due to the earlier start of movement, their elevating capacity.

BACKGROUND OF THE INVENTION 
The present invention relates to an elevator system in general and, in 
particular, to an elevator drive control device for smooth start-up. 
The conventional elevator system includes a hoisting motor with a driving 
pulley for carrying out linear motions and devices for the measuring of 
revolutions and of distances as well as a drive control with a control 
amplifier, setting means and actual transmitters for the speed and the 
distance, associated comparators as well as a control device for smooth or 
jerk-free start-up, where first the suppression of the start-up jerk is 
controlled and then a control according to preset distance/speed curves is 
performed. 
The start-up behavior of elevators is an essential criterion for the 
subjective judging of the feeling of the occupant, which in the start-up 
phase is determined basically by the acceleration as well as by the 
acceleration changes and eventual vibrations. In this case, every 
acceleration of the elevator car and thus that of the passengers results 
from the superposition of the forces acting in the elevator system 
according to the formula force (K) equals mass times acceleration. To be 
considered for the start-up in this connection are: the force of imbalance 
resulting from the difference between the car load and the counterweight, 
the braking force of the blocking brake, the friction force resulting from 
the friction resistances of the movable parts as well as the motor driving 
force resulting from the starting torque of the hoisting motor. As is 
generally known, there results during the start-up phase in some of these 
forces discontinuities in the derivative trend with respect to time. This 
relates to the braking force, because this force becomes suddenly zero on 
easing the mechanical blocking brake, as well as to the friction 
resistances of all movable masses and the transmission components at 
standstill which are considerably greater than during movement and thus a 
very sudden change occurs on start-up from standstill. These mechanical 
discontinuities take place too rapidly to be controlled with the normal 
drive control. On the contrary, they cause control technological 
discontinuities and act according to the formula force (K) equals mass 
times acceleration on the acceleration, which leads to strong changes in 
the acceleration, leading to "jerks". Elevators of all types of 
construction tend therefore to generate a "start-up jerk" when starting up 
from standstill. 
In the past, a multitude of devices were proposed in order to eliminate 
this disagreeable start-up jerk completely or partially and thereby to 
improve the comfort of travel. In this way, for instance, a device has 
become known from the German document open for inspection No. 31 24 018 
for the addition of weighing data to the control system of an elevator. It 
is the purpose of this device to compensate the imbalance torque, which 
acts from the load side at standstill and which is picked up by the 
blocking brake prior to the start-up by an appropriate motor torque, so 
that on release of the now relieved blocking brake no "jerky" start-up 
will take place. As a measure of the imbalance torque, the car load is 
measured directly and this weighing data impressed on the drive motor by 
way of the control system. This elevator control system is constructed as 
an operational amplifier circuit with a velocity control amplifier, the 
positive terminal of which is connected to ground and at the negative 
terminal of which the nominal or set point and the actual values of the 
velocity arrive and at which furthermore a stabilizing resistor and a 
stabilizing capacitor are connected in series from the negative terminal 
to the output of the velocity amplifier. For coupling of the weighing 
data, the stabilizing resistor is bridged by a starting switch and the 
weighing value conducted with an auxiliary starting switch to the 
connecting point between the stabilizing resistor and the stabilizing 
capacitor. With this a jerk-free start-up of the elevator shall be 
attained, without a separate weighing memory unit with a complex control 
being necessary. 
This device exhibits the basic disadvantage that only one of many different 
causes of the start-up jerk can be eliminated, that is, the sudden 
becoming active of the imbalance force on release of the mechanical 
blocking brake. Another cause for the start-up jerk, that is the unsteady 
derivative trend with respect to time of the friction resistances during 
the transition from static friction to sliding friction, cannot be 
eliminated or alleviated thereby in any way. However, such 
non-uniformities of friction are increasingly noticeable as start-up jerk 
in modern systems of low mass and, due to the elastic cable connection 
between the drive and the elevator car, easily lead to vibrations and 
oscillations. A further disadvantage of the device shown in German 
document open for inspection No. 31 24 018 is the fact that expensive load 
measuring devices are necessary, the accuracy of measurement and long term 
constancy of which is not sufficient in all cases. 
It is here that the invention tends to find a remedy. The proposed 
invention is therefore based on the problem of suppressing the start-up 
jerk in elevator installations and thereby improving their travelling 
comfort. In this case, the suppression of jerks shall be effective in both 
directions of travel and for any arbitrary loads and at arbitrary values 
of static and sliding fraction. The suppression of jerks according to the 
invention shall also be designed in such a manner, that the controlled 
elevator drives themselves are utilized for the suppression of jerks and 
that because of this only a modest additional expense will be required. 
SUMMARY OF THE INVENTION 
A first advantage of the invention can be seen in the fact that by the 
suppression of the start-up jerk, all the vibrations and oscillations are 
eliminated which are otherwise triggered by the jerk. This is of 
particular importance in elevator installations where the car and the 
drive are not connected rigidly, but are connected elastically by way of 
long cables and for this reason the whole assembly constitutes a weakly 
damped system capable of oscillation. A considerable inducement to 
oscillation for this system is eliminated and thus also the corresponding 
vibrations and oscillatory processes which delay the start-up procedure in 
time and would prejudice it with regard to comfort. 
Furthermore it has proven to be advantageous, that with the suppression of 
the jerk according to the invention the time interval between the travel 
command and the attainment of the nominal velocity is shortened. This gain 
in time is based on a two-fold economy of time: first the elevator car 
sets itself in motion earlier, because based on the initially increased 
nominal travel curb, according to the invention, the time of start-up is 
attained earlier, and second the subsequent upward travel can be made in 
the shortest possible time due to the absence of vibrations and building 
up of transient oscillations. During the start-up therefore no time is 
lost, which cannot be gained back later. This saving of time is of 
importance in elevator installations because it increases their conveying 
capacity. 
Additional advantages, realized with the invention according to the 
proposal, result from the circumstance that for the suppression of the 
jerk essentially the existing control device can be utilized and that the 
functions of the suppression of jerk and the control of speed are timewise 
separated, because first the jerk is being suppressed and only then the 
speed is controlled. This makes it possible to use the already existing 
drive control circuit in time multiplex twofold; up to the setting in 
motion of the elevator car for the suppression of the jerk and afterwards, 
in customary manner, for the control of the speed. For the suppression of 
the jerk thus only a modest additional hardware expense in necessary: 
namely an on/off switch as well as a set point value multiplier. These two 
circuits are function and not installation related. Thus, they can be 
constructed the same for every elevator installation. The matching to the 
friction conditions typical of an elevator installation is performed by 
the adjustability of the multiplication factor. It is obvious that this 
offers economic advantages; the expense for manufacture, installation and 
maintenance is reduced in price and in this way a cost-advantageous 
solution is obtained. The double utilization of the drive control circuit 
for the suppression of the jerk and for the velocity control also means 
that both these function are together function-efficient or fail together. 
In case of outage of the suppression of jerk therefore no drive is 
possible and thus also no start-up jerk which would have to be suppressed. 
Such a suppression of jerk can therefore be said to be fail-safe and 
exhibits correspondingly a very high reliability. It is also obvious that 
the earlier mentioned temporary multiplication of the set point value can 
be installed rapidly and simply into velocity controlled elevator drives. 
The invention according to the proposal is therefore eminently suitable 
for refitting customary elevator installations with velocity control with 
suppression of jerk units and to improve them subsequently in their travel 
properties. 
The invention will be described in the following in its application for the 
suppression of the start-up jerk in an elevator installation, however the 
principle forming the basis of this can be applied generally, if masses 
have to be driven by means of an electronic drive through elastic 
connecting links, as this is for instance often the case in mechanical 
conveying and handling in horizontal and vertical transports.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a conventional three phase drive 1 with a hoisting motor 2 
having a high speed winding 3 and a low speed winding 4. An output of the 
motor 2 is coupled to an input of a worm drive 5 and a driving pulley 6 
drives in known manner an elevator car 7 with a counterweight 8 in a shaft 
9. The motor 2 is controlled by an analog controller 11, by way of a three 
phase regulating unit 12 and a controlled rectifier 13. The set point 
values for the acceleration and deceleration are digitally stored in a set 
point memory 14 from where they are conducted to a set point input 15 of 
the analog controller 11. For the detection of the actual number of 
revolutions of the driving pulley 6, a digital tachometer 16 of the 
incremental transmitter type is coupled to a worm gear output shaft 17 and 
connected by way of a pulse shaper 18 and a low-pass filter 19 with a set 
point input 20 of the analog controller 11. In response to a call, the set 
point travel curves are generated from the set point memory 14 which is 
connected with an operating control 21 and a distance counter 22. The 
distance counter 22, in known manner, forms a car position signal by 
summing up the pulse frequency, which is proportional to the velocity, and 
for this is also connected with the pulse shaper 18. 
FIG. 2 comprises a diagram of the progress in time of the forces, as well 
as the actual start-up curves therefrom, in an elevator system according 
to FIG. 1, that is without the suppression of jerks. In this diagram, the 
motor driving force is designated with 26, and the corresponding set point 
start-up curve with 27. The force of friction is independent of the 
direction of travel and becomes at standstill the static friction R.sub.H, 
and during motion the sliding friction R.sub.G. At a load which is fully 
balanced by the counterweight there is generated for the resultant driving 
force diagram 28 and a corresponding actual start-up curve 29 at a time of 
start-up t.sub.G. At an imbalance U.sub.1 in the load in the direction of 
travel, the resultant driving force progresses according to a diagram 30 
with an associated start-up curve 31 and at a time of start-up t.sub.U1. 
At an imbalance U.sub.2 in the load against the direction of travel, a 
driving force diagram and an actual start-up curve are designated with 32 
and 33 respectively, at a time of start-up t.sub.U2. At the beginning of 
movement all actual start-up curves 29, 31, 33 have an identical start-up 
tangent 34 and exhibit about the same damped oscillation trend 35. 
The elevator drive equipped with the control device for jerk-free start-up 
according to the present invention is represented in the block diagram of 
FIG. 3. As in FIG. 1, a hoisting motor 2 is provided, which is driven by 
way of a three phase regulating unit 12 and a controlled rectifier 13. The 
actual speed of revolution of the pulley 6 is detected by a digital 
tachometer 16 and conducted to the pulse shaper 18, the output of which is 
conducted to the inputs of the distance counter 22 and the low-pass filter 
19. The hoisting motor 2 is controlled with respect to speed, for which 
purpose set point values forming the set point travel curves are stored 
digitally in the set point memory 14 as a function of the distance or 
path. For the interrogation of the set point value, the set point memory 
14 is connected with the operating control 21 and the distance counter 22 
and is also connected to generate the set point signal from its output by 
way of a multiplier 39 and a digital-analog converter 40, to a set point 
input 41 of a comparator 42. Furthermore, there exists a connection each 
from the output of the low-pass filter 19 to an actual value input 43 of 
the comparator 42, as well as from an output 44 of the comparater to an 
input of a PI-controller 45. An on/off switching circuit 46 is controlled 
at its start input 47 by a start or travel signal from the operating 
control 21, and at its stop input 48 by the digital tachometer 16 and is 
connected at its output with the set point value multiplier 39. A first 
control circuit 49 for the suppression of jerks as well as a second 
control circuit 50 for the control of the speed are embodied in the 
circuit elements 14, 39, 40, 42, 45, 12, 2 and 16 which are used twofold 
in a time multiplexed connection. 
Diagrams, which relate to the control device according to the invention as 
shown in FIG. 3, of force and velocity plotted against time are presented 
in FIGS. 4, 5 and 6. From this it is evident that the jerk due to friction 
can be suppressed completely in both directions of travel (FIG. 4), for 
all conditions of frictions (FIG. 5), and for all loads (FIG. 6). 
FIG. 4 shows the progress in time of the driving forces as well as the 
associated start-up curves at no, at partial and at total suppression of 
jerks. Here again the static friction is designated by R.sub.H, the 
sliding friction by R.sub.G and it is assumed that the car and the 
counterweight are balanced. If the multiplication factor "m" has the value 
of one, then the suppression of jerks is not effective, so that at the 
time t.sub.1, the resulting driving force 51 and the start-up curve 53 
yield the start-up tangent 54. At m=m.sub.1 greater than one, the 
corresponding designations at time t.sub.m1 are driving force 56, start-up 
curve 58 and tangent 59. At m=m.sub.o greater than one, the instability in 
the resulting driving force 61 is completely eliminated, so that the 
corresponding start-up curve 63 at the time t.sub.mo exhibits a horizontal 
start-up tangent 64. 
It is illustrated in FIG. 5 how the jerk suppression according to the 
invention can be matched to different friction conditions typical in 
elevator installations. Two states of friction are being distinguished, 
which are characterized by their pertinent static and sliding friction 
values R.sub.H1, R.sub.G1 and R.sub.H2, R.sub.G2. A total suppression of 
jerks is attained at R.sub.H1, R.sub.G1 with m=m.sub.o2 where the start-up 
curves 72 and 73 respectively result, both with horizontal start-up 
tangent 74. 
Furthermore, it is evident from FIG. 6 that the suppression of jerks 
according to the invention is equally effective in both directions of 
travel for all loads. Again, the static friction is designated with 
R.sub.H and the sliding friction with R.sub.G. At an imbalance U.sub.1 in 
the direction of travel there results from m=1 (suppression of jerk 
ineffective) the start-up jerk 75, the start-up curve 76 as well as the 
start-up tangent 77 and, from a set point value multiplication m=m.sub.U1 
greater than one, the start-up curve 78 with the horizontal start-up 
tangent 79. At an imbalance U.sub.2 against the direction of travel the 
corresponding diagrams are designated with 80, 81, 82, 83 and 84 
respectively. 
An expanded, general development of the jerk suppression according to the 
invention becomes evident from the block diagram of FIG. 7a. As an 
addition to the embodiment shown in FIG. 3, three set point/actual value 
feedback circuits 85, 86 and 87 are provided with controllers 88, 89 and 
90 , each comprising a set point value multiplier or amplifier 39. The 
on/off circuit 46 also acts through a multiplier 91, which increases the 
velocity set point value by way of the controller 90 in the outermost 
feedback circuit temporarily by the multiplication factor "m". As an 
alternative, the multiplier 91 can also be connected to the controller 88 
or the controller 89. The controller 89 corresponds to the controller 45 
in FIG. 3 and the controller 88 receives feedback from the hoisting motor 
2. FIG. 7b shows a comparison of customary start-up curves with 
suppression of jerks obtainable according to the invention, as per FIG. 
7a. In this diagram, a continuous curve is assumed, as is generally known 
from practice. Specified for customary drive controls are a set point 
start-up curve 92, which leads to an actual start-up curve 93 with a 
start-up time of t.sub.2 and a transient built-up 94. Contrary to this is 
the set point start-up curve 95 with the suppression of jerks according to 
FIG. 7a. The curve 95 follows during the first seven time increments a 
correction curve 96, and is therefore increased during a short interval 97 
and decreased along a curve 98 at the transition from static to sliding 
friction, wherefrom the desired actual start-up curve 99 will result, 
which has an earlier start-up time t.sub.3 and which does exhibit a 
transient build-up at a horizontal start-up tangent 100. For an 
explanation of the manner of functioning of the suppression of jerks 
according to the invention, reference shall be made to FIGS. 1 through 7b 
and assumed that an elevator car 7 in an elevator shaft 9 shall be set 
into motion from standstill by means of a speed controlled drive. 
First of all the conditions of prior art drive controls without the 
suppression of jerks according to the present invention are presented in 
the FIGS. 1 and 2, so that the character and the disadvantages of the 
start-up jerk are clearly apparent. Triggered by the operating control 21, 
the drive 1 will start where, for simplification a linear rise of the 
motor driving force according to diagram 26 will be assumed. Starting from 
a perfectly balanced load, the motor driving force 26 reaches at time 
t.sub.G the static friction force R.sub.H, which at the beginning of the 
movement assumes suddenly the value of the sliding friction R.sub.G, so 
that the difference between the motor driving force 26 and the sliding 
friction force R.sub.G will become effective as the resultant driving 
force 28 and, due to its instability at the time t.sub.G, will lead to a 
start-up tangent 34 and a transient oscillation 35. From the start of the 
motion at time t.sub.G, the tachometer pulses, which in each case 
correspond to a certain travel distance, are counted in the distance 
counter 22 and generate at the output of the set point value memory 14 
corresponding set point velocity values. These values are compared in the 
controller with the actual velocity value, corresponding to the frequency 
of the tachometer pulses. Depending on the result, either a driving torque 
is generated in the motor through phase chopping by way of the three phase 
controller 12, or the slow travel winding of the motor is supplied with 
direct current by way of the phase controlled rectifier 13, so that a 
retarding torque is created due to the eddy current effect. Starting from 
a linear nominal start-up curve 27, this start-up process leads to an 
actual start-up curve 29 with a start-up tangent 34 and transient 
oscillation 35. At an imbalance U.sub.1 in the direction of travel, the 
corresponding diagrams are designated with 30, 31, 34 and 35; and at an 
imbalance U.sub.2 against the direction of travel they are designated with 
32, 33, 34 and 35. In all three cases, there result similar set point 
start-up curves 29, 31, 33 which on account of equal unbalances of the 
driving forces 28, 30, 32 also exhibit equal start-up tangents 34 and 
equal transient oscillations 35, but which, due to the different 
equalization of the load by the counterweight, have different start-up 
times t.sub.G, t.sub.U1 and t.sub.U2 respectively. 
The function of the control device for jerk-free start-up shall now be 
explained in detail with the aid of the FIGS. 3, 4, 5, 6, 7a and 7b. First 
of all, it should be considered that according to the characterization of 
the invention, the specified mechanical start-up jerk is eliminated by 
control. Thus, in the block diagram of FIG. 3, two control circuits are 
recognizable; control circuit 49 for the suppression of jerks as well as 
control circuit 50 for the regular speed control. Of importance is that 
the suppression of jerks according to the invention, as well as the 
control of the speed of revolution of the pulley 6 do not take place 
simultaneously but successively: the suppression of jerks in the time 
interval from start to and with the beginning of motion, and the control 
of speed from the beginning of motion up to the end of the controlled 
rotation of the pulley. Based on this separation in time, the circuit 
elements 14, 39, 40, 42, 45, 12, 2, and 16 are utilized by both control 
circuits 49 and 50 in time multiplexed fashion. 
The basic control process for regulating or smoothing the jerk at start-up 
is described with the aid of FIGS. 3 and 4. The drive starts with the 
operating control 21 calling for a first set point input from the set 
point memory 14 and by setting the multiplication factor "m" of the set 
point multiplier 39 by way of the on/off circuit 46 to a value greater 
than one. The first set point value increased in this manner acts by way 
of the digital-analog converter 40, the comparator 42, the PI-controller 
43 as well as the three phase controller 12 on the hoisting motor 2, where 
a motor driving force is generated which runs up depending on the chosen 
multiplication factor "m" along the linearly assumed diagrams 52, 57 and 
62. When the motor driving force exceeds the static friction force 
R.sub.H, movement will begin. The digital tachometer 16, which also serves 
as a motion detector, detects this motion after a few hundred millimeters 
of movement of the drive pulley and thereby switches the on/off circuit 46 
to "off" by way of the stop input 48, and thus the multiplying factor "m" 
is changed back to one. This cycle can be traced in FIG. 4 as follows: at 
m=1, that is at no jerk suppression, the motor driving force runs up along 
the straight line 52. The beginning of the movement takes place at time 
t.sub.1, where the friction force, at unchanged increasing motor driving 
force 52, decreases suddenly from the static friction R.sub.H to the 
sliding friction R.sub.G . The resulting driving force 51 exhibits 
therefore a discontinuity with the amplitude R.sub.H -R.sub.G, which 
causes the highest possible friction jerk and leads to the start-up curve 
53 with the start-up tangent 54 and transient oscillation 55. 
At m=m.sub.1 greater than one, the motor driving force no longer proceeds 
rising monotonically, but its progress will be switched over for the 
purpose of suppression of jerks at the time t.sub.m1 from the initial 
diagram 57, to the diagram 52. The resulting driving force 56 exhibits at 
the time t.sub.m1 a discontinuity with the reduced amplitude K.sub.1 
-R.sub.G. Although the friction jerk is thereby only partially suppressed, 
the results from this in comparison to the conditions with m=1 are an 
improved start-up curve 58 with a less steep start-up tangent 59 and a 
reduced transient oscillation 60. At m=m.sub.o greater than one, the 
progress of the motor driving force at the beginning of the movement, that 
is at the time t.sub.mo, is switched over from the initial diagram 62 to 
the diagram 52 and the motor driving force is reduced by the amount 
R.sub.H -R.sub.G. The sudden reduction of the friction force at the time 
t.sub.mo from R.sub.G to R.sub.G is therefore completely neutralized by an 
equally large and approximately equally rapid reduction of the motor 
driving force. The associated multiplication factor m.sub.o is therefore 
an optimum with respect to the suppression of the jerk. The resulting 
driving force 61, at the time t.sub.mo, no longer exhibits any 
discontinuity so that the friction jerk is completely suppressed and a 
start-up curve 63 with a horizontal start-up tangent 64 without transient 
oscillation is present. 
It is furthermore illustrated in FIG. 5, how with the present invention a 
complete suppression of jerks is attained at arbitrary conditions of 
friction R.sub.H and R.sub.G. For first values of friction R.sub.H1, 
R.sub.G1 and no suppression of jerks (m=1), there appear the resultant 
driving force 66, as well as the start-up curve 67 with the start-up 
tangent 68. Now we set m=m.sub.o1, which completely eliminates the 
start-up jerk according to the diagrams 72 and 74. For arbitrary further 
values of friction R.sub.H2, R.sub.G2, the suppression of jerks takes 
place in an analogous manner. For this, it is only necessary to choose the 
multiplication factor "m" correspondingly, that is to set it equal to 
m.sub.o2. The associated diagrams are marked with 73 and 74. By 
appropriate choice of the multiplication factor "m", the control device 
for jerk-free start-up according to the invention, can therefore be 
matched to all conditions of frictions typical in elevator installations. 
Finally, it is shown in FIG. 6 how, with the present invention, the 
start-up jerk can be suppressed at arbitrary loads and in both directions 
of travel. Since in this general case no complete load equalization by the 
counterweight exists, two imbalances U.sub.1 and U.sub.2 are assumed; 
U.sub.1 in the direction of travel and U.sub.2 acting opposite to the 
direction of travel. For m=1, that is no suppression of jerk, the 
resultant driving force as well as the start-up curves progress as shown 
in diagrams 75, 76 and 77 at U.sub.1, respectively 80, 81 and 82 at 
U.sub.2. In both cases, the start-up jerk is a maximum with the amplitude 
R.sub.H -R.sub.G. This start-up jerk is in both cases completely 
suppressed by the appropriate choice of the multiplying factor "m". With 
m=m.sub.U1 and m=m.sub.U2, there results the desired start-up curves 78 
and 83 both with horizontal start-up tangents 79 and 84 respectively. 
In each of the drive controls shown in FIGS. 3 and 7b, the multiplier is an 
integral component of the drive control and can be adjusted to a selected 
multiplication factor greater than one. The multiplication factor value 
can be selected as a function of the car load and/or as a function of the 
elevator system friction. 
In accordance with the provisions of the patent statutes, the present 
invention has been described in what is considered to represent its 
preferred embodiment. However, it should be noted that the invention can 
be practiced otherwise than as specifically illustrated and described 
without departing from its spirit or scope.