Control device for stopping the operation of a single-phase asynchronous motor with a capacitor

The invention relates to a control device for stopping the operation of a single-phase asynchronous motor with a capacitor in the event an overload of this motor with respect to a threshold value is detected. This device is characterized in that it includes, on the one hand, device for measuring the phase shift between any one parameter, voltage or current (U1, U2, I2, I3) of the main phase (.phi.1) or the secondary phase (.phi.2) and another one of these parameters and, on the other hand, device for controlling the stoppage capable of interrupting the current supply to the motor in the event there is measured a time delay lower than a memorized threshold value.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The invention relates to a control device for stopping the operation of a 
single-phase asynchronous motor with a capacitor in the event of an 
overload of this motor with respect to a threshold value. 
(2) Description of the Prior Art 
As a matter of fact, nowadays there already exist devices capable of 
detecting a single-phase asynchronous motor is operating with an overload 
and, accordingly, of controlling the stoppage of this motor. More 
particularly, this device includes, on the one hand, a circuit capable of 
supplying a direct voltage similar to the voltage at the terminals of the 
phase-shift capacitor of the motor and, on the other hand, a circuit 
supplying a constant reference voltage. This assembly is completed with a 
comparator circuit which compares both voltages proceeding from the 
preceding circuits, in order to finally deliver a stop signal when the 
homothetic direct voltage becomes equal to or lower than the reference 
voltage. 
There is furthermore provided for the circuit capable of supplying the 
reference voltage to be subjected to the mains, so as to supply a voltage 
which is at any time proportional to the mains voltage, irrespective of 
the changes in this latter. 
As a matter of fact, such a device has a number of drawbacks associated to 
its lack of reliability, its long reaction time and the adjustments it 
requires with respect to the specific characteristics of each motor. 
In particular, the assembly is depending on the temperature of the motor in 
that this latter has an influence on the voltage at the terminals of the 
phase-shift capacitor. In addition, since this device is based on the 
principle of a comparison between direct voltages, any result can be 
derived only after a certain time corresponding to several alternations of 
the voltage at the terminals of said phase-shift capacitor has elapsed. 
Now, this delay at the level of the reaction time of the device can give 
rise to serious incidents. In particular, within the framework of the 
application of such a single-phase asynchronous motor to the control of 
the winding up and the unwinding of an apron of a roller blind. 
Thus, although this device for controlling the stoppage can also intervene 
for stopping the motor at the end of the winding up and the unwinding of 
the apron, it should be appreciated that such is possible only if one is 
ready to accept some restraints. Namely, when winding up the apron of the 
roller blind and arriving at the upper end of the path, it is most likely 
that the delay in the control to stop the motor results into the 
tensioning of the apron, whereby the hinged connections between two 
consecutive slats of the apron get under a heavy strain. Since a same 
motor is frequently used for roller blinds of different sizes, this 
putting under strain resulting from the delay in stopping an eventually 
overpowered motor can cause the apron to break 
In the opposite case, when unwinding the apron of the roller blind, this 
delay in controlling the stoppage of the motor at the lower end of the 
path results into the putting under strain of the device for impeding the 
winding-up of the apron of the roller blind this latter is generally 
provided with. Thus, here too, this putting under strain of such a device 
for impeding the winding-up comprised of specific hinging means connecting 
the winding-up shaft to the first slat of the apron can be larger than the 
mechanical strength of the assembly. 
The solution could eventually consist in adjusting the threshold defined by 
the constant reference voltage acordingly, so as to make the device more 
sensitive. However, because of a change, even though rather slight, in 
voltage at the terminals of the phase-shift capacitor with respect to the 
torque of the motor, the device for controlling the stoppage may not be 
made too sensitive, for otherwise the slightest resistance due to the 
frictions experienced by the apron during its winding-up or its unwinding 
would cause the motor to unexpectedly stop. 
Finally, this known device for controlling the stoppage inevitably depends 
on the characteristics of the motor and, in particular, on the capacitance 
of the phase-shift capacitor, but also on the mains voltage, so that 
adjustments systematically have to be carried out. This is of course a 
constraint when designing the device, but above all there may therefore 
exist a disadjustment in the course of time. Therefore, such a device for 
controlling the stoppage in addition proves to be unreliable. 
From U.S. Pat. No. 5,151,638 is also known another device capable of 
detecting a motor is operating in conditions of overload. To this end, 
this device monitors the phase angle between the voltage and the total 
current at the terminals of the motor. As a matter of fact, there is 
stated, within the framework of this document, that the phase angle tends 
towards zero when the motor load increases. Thus, according to this known 
device, there has been provided for detecting the zero passage of this 
voltage and the current, adequate means being then capable of providing a 
signal representative of the time delay between these latter. In 
particular, a ferromagnetic core is used to detect the zero passage of the 
current. 
As a matter of fact, it should be appreciated that the phase-shift 
measurement is performed on the voltage of the mains supplying the current 
to the motor and on the total current flowing through this latter. Now, if 
there is indeed a relationship between the phase shift of this voltage and 
this total current, on the one hand, and the motor load, on the other 
hand, this is not systematically a proportional relationship. In addition, 
it strictly depends on the characteristics of the motor. This means that 
these devices must be adjusted according to the motor being controlled, 
and this through test and other operations. This only increases their cost 
price. In addition, as soon as there is a need for adjustment, there 
exists a possibility of disadjustment, so that the device proves 
unreliable. 
SUMMARY OF THE INVENTION 
This invention is aimed at coping with all the above-mentioned drawbacks, 
this through a very highly accurate device for stopping the operation of a 
single-phase asynchronous motor capable of almost instantaneously 
detecting an overload of the motor with a view to interrupting the current 
supply to same. This accuracy also results from the fact that the 
overload-detection threshold is almost independent from the parameters of 
the motor, such as the capacitance of the phase-shift capacitor or even 
the operating temperature of this motor. 
To this end, the invention relates to a control device for stopping the 
operation of a single-phase asynchronous motor with a capacitor in the 
event an overload of this motor with respect to a threshold value is 
detected, characterized in that it includes, on the one hand, means for 
measuring the phase shift, thus the time delay, between any one parameter, 
voltage or current, corresponding to the main or secondary phase and 
another one of these parameters and, on the other hand, means for 
controlling the stoppage capable of interrupting the current supply to the 
motor in the event there is measured a time delay lower than a threshold 
value, preferably of the type which can be be set as a function of 
parameters in the memory. 
Finally, the object of the invention consists in measuring the time delay, 
not between the voltage at the terminals of the motor and the total 
current flowing through this latter, but between parameters, voltage or 
current, corresponding to the main phase and/or the auxiliary phase of 
this motor. Thus, one appreciates that internal parameters of the motor 
and not merely those capable of being measured on the current-supply wires 
of same are taken into consideration. This has the advantage of leading to 
a proportional relationship between the phase-shift measurement performed 
and the load applied on the motor. This results into the device becoming 
almost independent from the parameters of this latter, in particular from 
the capacitance of the phase-shift capacitor or also from the operating 
temperature of said motor. In addition, it is insensitive to the changes 
in mains voltage within a normal range. 
In addition, the control device according to the invention has an almost 
instantaneous reaction time, since it is capable of detecting an overload 
of the motor pursuant to measurements performed on one alternation. 
According to another feature of the invention, the threshold value can be 
set as a function of parameters and the device includes means for 
determining the evolution of the phase shift between the parameters being 
compared, with a view to detecting a sudden change in this evolution by 
calculating its derivative and to controlling the stopping of the 
operation of the motor. 
In some way, there is not merely detected whether the phase shift is lower 
or higher than a fixed value corresponding to the situation in which the 
motor delivers a maximum allowed torque, but there is looked for an 
abnormal evolution of this torque transmitted by the motor due to a 
suddenly larger (or smaller) resistance torque experienced by this latter. 
In such a case, the stoppage of the operation of said motor will in 
particular be controlled even before its maximum allowed torque occurs. 
When considering the very particular case of the roller blinds, one 
appreciates that it is usual, for reasons of standardization of the parts, 
but also because of the manufacturing costs of a small-sized motor, to use 
a same motor of a given power for a range of roller blinds. In this case, 
there exists the possibility of adjusting the phase-shift threshold value 
causing the stoppage of the motor as a function of the power to be 
provided in particular by this latter in order to achieve the winding up 
of the apron of the roller blind. This proves particularly constraining, 
the more it is known that the roller blinds are often manufactured to 
measure and according to the orders being received. In such circumstances, 
it is necessary to proceed to the adjustment of the detection threshold 
individually for each motor before its fitting onto a given roller blind. 
However, even in such circumstances, the control device is capable of 
acting on the operation of the motor only when this latter delivers a 
torque from which results a phase shift smaller or larger, as the case may 
be, than said threshold value. Thus, since the control of the stoppage at 
the end of the winding-up of the apron is concerned, one first observes 
that during this final phase of winding-up the motor meets nearly no 
resistance. Then, when the stops located on the end slat of the apron come 
in abutment, the motor produces on said apron a minimum torque, at the 
maximum allowed torque. At that time, the exceeding of the phase shift 
measured with respect to the threshold value causing the motor to stop is 
detected. It is obvious, under such circumstances, that the apron gets 
under a heavy strain under the action of said motor, in particular as far 
as the end slat is concerned, the stops of which accordingly rest on the 
abutment parts. 
This invention in particular allows to avoid this, since the device is 
capable not only of detecting the exceeding of a threshold value by the 
phase shift, but a sudden change of this phase shift which is also used 
for controlling the stoppage of the operation of the motor, and this even 
before it has had the time to produce the maximum allowed torque. Such a 
feature therefore allows to avoid any risk of deterioration of the roller 
blind in the event of any clamping, irrespective of the power of the motor 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention relates to a control device 1 for stopping the operation of 
an asynchronous motor 2 with a capacitor 3, as shown in FIG. 1. An 
embodiment of such a device 1 is shown in FIG. 2. 
Thus, this motor 2 is characterized by a main coil B1 and an auxiliary coil 
B2, on the one hand, connected to the common terminal 4 of the mains S 
and, on the other hand, connected to each other through the phase-shift 
capacitor 3 capable of creating the rotating field for controlling the 
rotation of the motor. In this respect, it should be appreciated that this 
main coil B1 is also connected to the terminal 7 of the mains S 
corresponding to the main phase .phi.1. 
As regards the device 1 for controlling the stoppage, it is aimed at 
detecting an eventual overload of the motor 2 with respect to a threshold 
value, preferably of the type which can be set as a function of 
parameters. The device 10 serves to almost instantaneously control the 
stopping of the operation of this motor 2. 
For this purpose and according to the invention, the device 1 for 
controlling the stoppage includes means 8 for measuring the time delay 
and, thus, the phase shift between any one parameter, voltage U1, U2 or 
current I2, I3, of the main phase .phi.1 corresponding to the main coil B1 
or of the secondary phase .phi.2 corresponding to the auxiliary coil B2 
and another one of these parameters U1, U2, I2, I3. 
In order to make easier the understanding of this invention, the 
description which follows more particularly relates to the embodiment 
shown in FIG. 2 which corresponds to the case in which the device 1 
includes means 8 for measuring the time delay between the mains voltage U1 
and the current I2 flowing through the main coil B1, thus between the 
parameters of the main phase .phi.1. However, later within the framework 
of this description will be set forth how to measure the phase shift 
existing between other ones of these parameters of the main phase .phi.1 
and of the secondary phase .phi.2. 
Thus, according to the embodiment shown in FIG. 1, these measuring means 8 
include means 9 for detecting the voltage of the main phase 41 (the power 
supply voltage) as it reaches a predetermined threshold, preferably 
substantially zero. The measuring means 8 also includes a means 10 for 
detecting the current 12 flowing through the main coil B1 when it reaches 
a predetermined threshold, preferably substantially zero. It should be 
appreciated that when the detection of the passage at substantially zero 
of a voltage or a current is preferred to measure the phase shift, this is 
simply because this solution leads to easiness, since it allows to become 
independent from the difference in scale existing between both parameters 
being compared. However, the detection of the passage at any threshold 
whatsoever may of course be contemplated and gives rise to no problem at 
all when the parameters being compared are of the same nature 
(voltage/voltage; current/current). 
The device 1 furthermore includes a microprocessor 11 connected to a clock 
12 and which is capable of measuring a time delay, with a view to 
comparing same to a known threshold value of a memory 13 and which is, 
preferably, of the type which can be set as a function of parameters, this 
in order to control, should the case arise, the stoppage of the motor 2 
through appropiate control means 14. The time delay that the 
microprocessor measures is to be described hereinafter. 
It should be appreciated that the device furthermore includes a low-voltage 
direct-current supply 19 which namely intervenes in the control of the 
microprocessor 11. In particular, at the level of the circuits of this 
low-voltage direct-current supply 19 are to be found means 17 for lowering 
the voltage and the power, these means 17 being in particular defined by a 
resistor 18A and a capacitor 18B. Then, this assembly is associated to a 
current-rectifying circuit 20 of classical design preceding a voltage 
control 21. Accordingly, at the outlet of this latter is available a 
low-voltage direct-current supply capable of intervening within the 
framework of the logical commands received or transmitted by the 
microprocessor 11. 
As regards the detection means 9, they consist of a circuit 15 capable of 
converting the sinusoidal signal of the mains voltage, as schematically 
shown in FIG. 3, into a substantially square signal where each voltage 
jump corresponds to the passage at approximately zero of the voltage U1. 
This substantially square signal is adapted to form a 0- or 1-type logical 
command capable of being interpreted by the microprocessor 11. 
To this end, the terminal 4 of the mains S corresponding to the main phase 
.phi.1 supplies with current, through a dividing bridge R1/R2, the base of 
a NPN transistor 23 which is conductive when the voltage U1 is positive 
and is, on the other hand, locked when the voltage U1 is negative or zero. 
Accordingly, as soon as this voltage U1 becomes positive, this NPN 
transistor 23 connects the pin 24 of the microprocessor 11 to the earth 
corresponding to a logical command at the zero state. On the other hand, 
in the event of a negative or zero voltage, the NPN transistor 23 is 
locked, so that the pin 24 of the microprocessor is connected to the 
low-voltage supply 19 corresponding to a 1-state logical command. 
Reverting to the general design of the device 1 which provides for the 
possibility of measuring the phase shift between different parameters of 
the main phase .phi.1 and the secondary phase .phi.2, it will be 
appreciated that FIG. 8 is a simpliefied illustration of these detecting 
means 9 applied to any phase whatsoever to detect the zero passages of a 
voltage U1 or U2 in this phase. Thus, here the dividing bridge R1/R2 
through which the base of a NPN transistor is supplied with current is 
also to be found. 
As regards the means 10 for detecting the zero passage of the current I2 in 
the main phase .phi.1 and thus flowing through the main coil B1, they 
include an optocoupler 25 comprising a LED diode 26 which, when it is 
conductive and, thus, when a current is flowing through same, causes the 
biassing of the base of a NPN phototransistor 27, in order to make this 
latter conductive. At that time, a pin 28 of the microprocessor 11 being 
connected to the earth detects a 0-state of logical command. 
In the opposite case, i.e. when the LED diode 26 is locked, the NPN 
phototransistor 27 is, in turn, locked, so that the pin 28 is then 
connected to the low-voltage supply 19, giving rise to a 1-state logical 
command. It will be easily undertood that instead of using a NPN 
phototransistor 27, one may use a PNP phototransistor, reversing e.g. the 
mounting of the LED diode 26 in the circuit. 
This optocoupler 25 is mounted in parallel, at a diode-current shunt 29, on 
the electric connection 30 connecting the main coil B1 to the terminal 7 
of the mains S. 
Thus, through this optocoupler 25 is transmitted to the microprocessor 11 a 
substantially square signal (see FIGS. 5 and 6) each transition of which, 
similar to the changing of a logical command from the 0-state to the 
1-state, or vice-versa, corresponds to the passage at substantially zero 
of the current flowing, in this case, through the main coil B1. 
Here too, these detecting means 10 are shown in their general design for 
measuring a current I2 or I3 flowing through the main phase .phi.1 or the 
secondary phase .phi.2 in FIG. 7 of the attached drawings. There can be 
seen in particular the presence of this optocoupler 25 which is supplied 
with current by a diode-current shunt 29. 
Therefore, according to the parameters the phase shift of which one wants 
to determine, use will be made, depending on the case, of detecting means 
9, as shown in FIG. 8, associated to the main phase .phi.1 and/or to the 
secondary phase .phi.2 or detecting means 10, as shown in FIG. 7, which 
can also be associated to said main phase .phi.1 or to said secondary 
phase .phi.2. 
Thus, when it is desired to measure the phase shift between the voltage U1 
of the main phase .phi.1 and the current I2 of the main phase .phi.1, a 
combination of detecting means 9, 10, as shown in FIG. 2, is chosen. 
Within the framework of the measurement of the phase shift between the 
voltage U2 in the secondary phase .phi.2 and the current I3 in the 
secondary phase .phi.2, this combination of detecting means 9, 10, as 
shown in FIG. 1, is also used, but in particular applied to said secondary 
phase .phi.2, thus to the auxiliary coil B2. 
Within the framework of the measurement of the phase shift between the 
voltage U1 in the main coil B1 (main phase) and the voltage U2 in the 
auxiliary coil B2 (secondary phase), detecting means 9, as shown in FIG. 
8, will be applied to each phase. 
Finally, when the phase shift between the current I2 flowing through the 
main coil B1 and the current I3 flowing through the auxiliary coil B2 is 
to be measured, it is convenient to associate to each phase detecting 
means 10 corresponding to the diagram in FIG. 7 and making use, in 
particular, of an optocoupler which has the advantage of providing a 
galvanic insulation between the mains current-supply and the current 
supply of the microprocessor 11. 
Finally, through these square-shaped signals delivered by said detecting 
means 9, 10, it is easy for the microprocessor 11, thanks to the clock 12, 
to measure at each alternation the delay between both parameters taken 
into consideration to measure the phase shift and to compare same to a 
time corresponding to a threshold value, preferably, which can be set as a 
function of parameters. It should however be appreciated that during the 
transitory phases corresponding to the starting of the motor 2 
fluctuations occur at the level of this phase shift. Thus, in order to 
prevent the device from causing unexpected stoppages of the motor 2, there 
is provided for the means 8 for measuring the time delay not to be 
operative during these transitory starting periods. More exactly, the 
measurements performed or are interpreted by the microprocessors 11 only 
after a given time similar to this phase of starting of the motor 2 has 
elapsed, which time preferably corresponds to a determined number of 
alternations of the voltage U1, U2 or of the current I2, I3. 
After this transitory period has elapsed, the measuring means 8 fully play 
their role, so that in the event of a given phase shift the device 1 
controls the stopping of the operation of the motor 2. 
As a matter of fact, as already stated above, the reference threshold value 
is of the type which can be set as a function of parameters. The purpose 
being to be able to stop the motor 2 not merely when it is brought to 
produce a torque larger than a given limit value, but also when, during an 
operation cycle, there is observed a sudden and abnormal increase, or even 
decreases, of the torque produced by the motor. When taking the example of 
a motor-driven roller blind and when considering the more specific case of 
the cycle of winding-up of the apron, from an unfolded position to a fully 
wound-up position, it is known that, because of a progressive reduction of 
the weight of said apron, the motor is brought to produce a progressively 
smaller torque. Accordingly, when this this torque suddenly tends to 
increase during this cycle, this means that there exists a clamping in the 
path of the apron. Now, when the device is capable of controlling the 
stoppage of the motor only in the event a fixed threshold value is 
exceeded, the motor will necessarily continue to run, until it produces 
the maximum allowed torque. Now, within the framework of a clamping in 
particular of the path of a slat of the apron, this latter might not 
withstand this power transmitted by the motor 2. Earlier in the 
description has also been set forth the problem of the arrival at the 
upper end of the path of the apron where the motor normally produces a 
minimum torque. 
In order to cope with these drawbacks, the control device 1 according to 
the invention in addition includes means for determining the evolution in 
the course of time of the phase shift betweeen the parameters being 
compared, with a view to measuring a sudden change in this evolution and 
to controlling the stopping of the operation of the motor 2 when detecting 
such a sudden change in this phase shift. 
Thus, the function of these determination means associated to the 
microprocessor 1 is to calculate the gross derivative Db which is obtained 
by substracting from the phase shift measured at a given time the 
previously measured phase-shift value. According to a first embodiment, 
when the value of this derative is higher than a threshold value (called 
derived threshold) in the memory 13, it is inferred that there is an 
abnormal evolution of the phase shift and, hence, an obligation to stop 
the motor 2. 
However, within the framework of this process of determining the evolution 
of the phase shift it should be appreciated that the calculation of the 
gross derivative Db at a given time can be heavily influenced by a cause 
which is not actually due to a sudden increase of the torque produced by 
the motor 2. Thus, during the measurement, electronic noise and other 
influential parameters may interfere. 
To this end, it is preconized, according to the invention, to proceed to 
the calculation of a sliding derivative Dg(x) which consists in adding to 
the calculation of the gross derivative Db determined in the 
above-mentioned conditions the value of the sliding derivative Dg(x-1) 
previously calculated, which will be multiplied by a given filtration 
coefficient. This is thus an iterative function and when calculating the 
sliding derivative Dg(x+1) corresponding to the following measurement, 
this sliding derivative Dgx which has just been calculated and to which 
will be applied the filtration coefficient will be taken into 
consideration. In this respect, during the first phase-shift measurement 
after the transitory operation period, the measurement of the sliding 
derivative Dg1 corresponds to the gross derivative Db1. As regards the 
sliding derivative Gd2 determined at the next point, this will accordingly 
correspond to the gross derivative Db2 determined at that moment, plus the 
gross derivative Db1 at the previous moment multiplied by said filtration 
coefficient. 
Finally, the stoppage of the motor will be controlled only when the sliding 
derivative is higher than a threshold value, which allows to guarantee, in 
some way, that the evolution of the curve effectively goes in the 
undesired direction, in that not only the gross derivative at a given 
moment, but also the one which has been calculated during one or several 
preceding alternations are taken into consideration. Thus, the function 
applied for the calculation of this sliding derivative at a given point is 
of the type: 
EQU Dgx=A.Dbx+A'.Db(x-1)+A".Db(x-2) etc... 
where Dgx: sliding derivative at point x 
Dbx: gross derivative at that point x 
A, A', A" etc . . . : coefficient. 
It should be noted that this function may be so defined that only the gross 
derivatives corresponding to a limited number of points are effectively 
taken into consideration. It should be appreciated that the phase shift 
can be determined on one alternation, this operation can be repeated on 
each alternation, as well as the sliding derivative can be determined with 
the same periodicity. 
Thus, the control to stop the motor 2 can be obtained, on the one hand, 
when the phase shift between two parameters of said motor 2 exceeds a 
given threshold value and, on the other hand, when the sliding derivative 
Dg of the evolution curve of this phase shift is itself higher than a 
threshold value, which in particular allows to control this stoppage of 
the motor in the event of an abnormal disfunctioning of this latter and 
this even before it reaches the maximum allowed torque. 
As stated above, the interruption of the operation of the motor 2 is 
obtained through means 14 mainly including a triac 32. This triac 32, 
which is preferably mounted on the electric connection 30 connecting the 
main coil B1 to the terminal 7 of the mains S, is supplied with current 
when the logical command proceeding from the microprocessor 11 is in the 
0-state. This mounting is preferable, in that it leads to a lesser energy 
consumption. A reversed mounting could also be contemplated. 
Reverting to the situation corresponding to FIG. 2 of the attached 
drawings, when the microprocessor 11 detects a time delay smaller than the 
threshold value in memory 13 or when it detects an abnormal evolution of 
the phase-shift time between both parameters being measured, it transmits, 
through its pin 33, a 1-state logical command. More specifically, it 
supplies current to the base of a NPN transistor 34 connecting the base of 
a PNP transistor 35 to the earth. This latter is than locked, whereby it 
does no longer supply current to the triac 32 which interrupts the 
electric connection 30 connecting the main coil B1 to the mains S. 
As stated above, depending on the direction of rotation imparted to the 
motor 2, either coil B1, B2 becomes the main coil. Therefore, in order for 
the device 1 for controlling the stoppage to be able to intervene, 
irrespective of the direction of rotation imparted to the motor 2, it is 
necessary to divide into two sets the detecting means 10 mounted in series 
on each of the electric connections connecting the coil B1, B2 to the 
mains S through a RT relay for controlling the reversal of direction. 
However, according to a preferred embodiment, the device 1 for controlling 
the stoppage includes a RT relay 36 capable of controlling two contacts 
37, 38 which connect, as the case may be, coil B1 or coil B2 to the mains 
S through the electric connection 30 including the detecting means 10. 
Simultaneously, the other coil B2, B1, respectively, is converted, through 
these contacts 37, 38 into the auxiliary coil. 
The control of the RT relay 36 is ensured through a logical command 
transmitted by the microprocessor 11 which itself receives a logical 
command transmitted through normally open monostable pushbutons M and D 
39, 40. 
Thus, in the case the microprocessor 11 has received, during the preceding 
control, a 1-state logical command proceeding from the pushbutton M 39 and 
it now receives a 1-state logical command proceeding from the pushbutton D 
40, it transmits a 1-state logical command to a NPN transistor 41 the base 
of which is then biassed. Since the NPN transistor is conductive under 
these circumstances, it connects the RT relay 36 to the earth, which relay 
is furthermore connected to the common terminal 4 of the mains, so that it 
is supplied with current, causing the switching over of the contacts 37, 
38 and the reversal of the direction of rotation of the motor 2. 
It should be reminded, at this point, that though the description in 
particular relates to the embodiment shown in FIG. 2 and corresponding to 
the case in which the phase shift is measured between the voltage U1 and 
the current I2 of the main phase .phi.1, the situation is identical when 
different parameters are compared as to their phase shift. 
In short and as stated above in the description, taking into consideration 
the proportional relationship existing between, on the one hand, the time 
delay between one parameter, current or voltage, of the main phase .phi.1 
or the secondary phase .phi.2 of the motor and another one of these 
parameters and, on the other hand, the load of said motor, which load is 
in addition independant from the characteristics of this latter and namely 
from its temperature or also from the capacitance of the phase-shift 
capacitor, it has been possible to achieve a device for controlling the 
stoppage leading to an almost instantaneous reaction time and to a so far 
never achieved accuracy. 
In addition, since this device has the possibility of determining an 
abnormal evolution of the curve corresponding to the phase shift between 
the parameters being compared during a given operation cycle, it allows to 
avoid an eventual deterioration of the equipment. 
In particular, this invention will find an advantageous application in the 
field of the motorization of roller blinds which give rise to a large 
number of problems either during the apron-winding-up or unwinding cycles 
or also for controlling the stoppage of the motor at the end of the path. 
Finally, this invention actually allows to contemplate this stoppage of the 
motor at the upper and lower end of the path of the roller blind without 
there being any risk of a breakage of the apron e.g. due to the delay in 
controlling the stoppage which is usually carried out by the hitherto 
known devices. 
In addition, the device is capable of detecting a failure of the components 
of the motor. Thus, the short-circuiting of the capacitor inevitably 
causes a phase shift which lies beyond the standard values. In particular, 
this phase shift tends to abnormally evolve when taking into consideration 
the derivative of the curve. In the same way and for the same reasons, the 
device is capable of detecting a short-circuit at the level of the coils 
B1, B2. 
It should be appreciated that for the time being and in the absence of such 
a device according to the invention, such a short-circuit in the capacitor 
or the coils results into a heating-up of the motor, until the 
interruption of its supply with current occurs through the thermal safety 
this kind of asynchronous motor with a capacitor is usually provided with 
according to the standards applicable. 
In comparison, thanks to the device according to the invention, the thermal 
safety is not activated in the event of a default which is detected before 
the motor is completely deteriorated. 
Finally, thanks to this invention, it is possible, within the framework of 
the specific application to motor-driven roller blinds, to use, also for 
small-size roller blinds, a motor which is normally intended for 
large-size roller blinds without there being any risk whatsoever of 
deteriorating same due to this motor being overpowered. This not only 
allows a standardization at the level of the products, but also avoids the 
manufacturing of small-size motors which are often of a higher cost price.