EP1674655A1 - Method of determination of the position of the shaft of a motor for driving a roller shuter and actuator for its operation - Google Patents

Abstract

The method involves detecting and counting commutations produced between brushes and commutator segments for determining a position and/or speed of a shaft of motor (MOT) when the counting of the commutation is valid. Counter electromotive force of the motor is measured for determining the position and/or speed of the shaft when the counting of commutation is not valid. An independent claim is also included for an actuator for maneuvering movable unit of building.

Description

The invention relates to a method for determining the position and / or the speed of the shaft of a DC motor comprising an armature fed via brushes and a blade commutator and intended for driving an element. mobile building. It also relates to an actuator for the implementation of such a method.

Some actuators for moving elements such as doors, gates, shutters, blinds, projection screens, ventilation hatches fitted to buildings, include DC motors with power brushes. armature.

To control the maneuvers of these moving elements, it is interesting to know their position in order to determine when the engine power must be cut at the end of travel of the element or when it is in the intermediate position.

From US Pat. No. 5,038,087 there is known a method applying to a DC motor with brushes on the armature making it possible to determine by counting the extended position of a blind whose wound position is detected by stopping the motor. The calculation of the position is performed by counting commutations of commutator blades on the motor brushes. However, such a counting method is unreliable, especially when the motor is operating at low speed or when empty.

Application EP 1 333 150 discloses correction procedures which make it possible to partially solve the problems posed by such methods.

The unreliability is accentuated in applications where the motor supply voltage is provided by a converter powered on the commercial AC grid, for example 230 V, 50 Hz. In fact, the low-cost converters radiate a non-conductive component. negligible, at least at twice the frequency of the alternative network. When the frequency of these radiated parasites is close to the switching frequency of the brushes: their discrimination is very difficult or impossible.

Chopper devices for reducing the speed or power of the motor when the movable element arrives near a stopping position also constitute a significant source of noise.

Furthermore, it is known from US Patent 6,236,175 a method for measuring the speed of a DC motor from the measurement of the electromotive force against the motor. However, the coefficient of force against electromotive force KEMF, reflecting the proportionality between the electromotive force against the engine rotation frequency, is not constant from one engine to another, nor for the same engine, in fact. particular because it depends on the magnetic flux created by the inductive magnets and that this flux decreases very significantly with the temperature. However, in a gate application or garage door, the engine temperature may vary, in winter, from -15 ° C to + 80 ° C in a few operating cycles.

The object of the invention is to provide a method for determining the position and / or the speed of rotation of a motor shaft which obviates the drawbacks mentioned and provides improvements over the known methods of the prior art. . In particular, the method according to the invention makes it possible to accurately calculate by counting the position and / or the speed of rotation of an engine. The object of the invention is also to provide an actuator for carrying out this method.

• détecter et compter les commutations se produisant entre les balais et les lames de collecteur pour déterminer la position et/ou la vitesse de l'arbre du moteur lorsque le comptage des commutations est valide et
• mesurer la force contre électromotrice du moteur pour déterminer la position et/ou la vitesse de l'arbre du moteur lorsque le comptage des commutations n'est pas valide.

The method according to the invention is characterized in that it comprises the following phases:

• detect and count the commutations occurring between the brushes and the collector blades to determine the position and / or the speed of the motor shaft when the counting of the commutations is valid and
• measure the electromotive force of the motor to determine the position and / or the speed of the motor shaft when the counting of the commutations is not valid.

Different embodiments of the method are defined by the dependent claims 2 to 10.

The actuator according to the invention allows the operation of a movable element of the building. It comprises a DC motor having an armature fed via brushes and a commutator with blades and means for counting the commutations between the brushes and the commutator blades. It is characterized in that it comprises means for measuring the electromotive force against the motor and means for inhibiting the use of the switching counting means or the use of the electromotive force measurement means. motor to calculate the position and / or speed of the motor shaft.

The attached drawing shows, by way of example, an embodiment of the determination method according to the invention and an embodiment of an actuator according to the invention.

Figure 1 is a diagram of an embodiment of an actuator according to the invention.

FIG. 2 is a diagram illustrating the principle of the determination method according to the invention.

Figure 3 is a flow chart of an embodiment of the determination method according to the invention.

ACT actuator shown in Figure 1 is intended to drive a movable element LD equipping a building. It comprises a MOT motor type winding rotor rotor type, with collector and brushes. The inductor is preferably constituted by permanent magnets to the stator. The motor is kinematically connected to the movable element by means of a BRK release brake which makes it possible to immobilize the motor shaft when the motor is not powered in order to prevent it being driven by load. The motor is also connected to the load via a gear reducer GER.

MOT motor is powered from a DC voltage DC, provided by a battery or a converter not shown. This voltage UDC is applied to the motor terminals by power control means comprising a CPU microcontroller controlling unrepresented switching means for rotating the motor in a first direction or in a second direction. The microcontroller is connected to a not shown order receiver for detecting orders issued following an action performed by a user or following an event detected by an automated system.

One of the functions of the control means is to cut off the power supply of the motor when the shaft thereof has reached a position particular, corresponding for example to a predefined intermediate position or an end position of the movable element LD.

The position of the motor shaft, and therefore that of the driven moving element, is measured by counting. The control means also cause the stopping of the motor supply and possibly a short instant of reverse supply to allow a reverse movement of the movable element in case of detection of an obstacle. This obstacle detection can, for example, be carried out by detecting an abnormal deceleration of the motor. The control means must therefore make it possible to calculate the position and the speed of the movable element as precisely as possible.

The microcontroller has an output 01 for controlling the frequency or the duty cycle of a controlled switch TRU connected in series with the motor. This controlled switch is for example a MOS transistor whose gate is connected directly to the output O1 of the microcontroller. This output is for example a PWM type output. The operation of the switch is of the step-down type: the armature voltage UM applied to the motor armature has a mean value lower than the supply voltage UDC. Thus, it is possible to initiate reduced voltage operating phases and to produce ramps for increasing voltage or decreasing voltage in order to carry out phases of acceleration or progressive deceleration of the motor.

The armature current IM is measured using a shunt resistor RS of low value, a terminal of which is connected to a first motor armature terminal and to the GND electrical ground. Thus, the measurement voltage URS at the terminals of the shunt is low compared to the supply voltage of the motor UDC. A detection device comprising at least one comparator CMP makes it possible to transform into a two-level logic signal (up and down), the armature current fluctuations IM caused by commutations of the collector blades as they pass opposite the brushes.

The output C3 of the comparator CMP is connected to a first input 11 of the microcontroller. This input is of digital type: the logic pulses correspond to commutations of the collector. These pulses are summed algebraically (counted positively when the motor rotates in a first direction and counted negatively when the motor rotates in a second direction in a counter CNT which consequently gives the image of the position of the movable element. pulses is also calculated, this frequency is the image of the instantaneous speed of the motor and thus of that of the mobile element.This frequency is stored in a memory FRQ of the microcontroller.

A second input 12 of the microcontroller is of analog type. This is for example the input of an analog digital converter built into the microcontroller. The second input 12 is connected to the second armature terminal of the motor. Since the ground of the circuit is connected to the first armature terminal of the motor, the voltage measured by the analog-digital converter is therefore the armature voltage UM of the motor.

It is known that this voltage is strictly equal to the electromotive force as soon as the armature current IM is zero, that is to say when the controlled switch TRU is open for a sufficient time. The periodic opening of the controlled switch TRU therefore allows the precise measurement of the electromotive force against the motor, the value of which is stored in a memory referenced EMF.

FIG. 2 diagrammatically represents the area of validity of the pulse measurement result at the output C3 of the comparator CMP.

There is at least one zone where the signal of the output C3 can not be validly considered for calculating the position and / or the speed of the motor shaft: either because of a low signal-to-noise ratio, or because the motor is slightly driven by the load and absorbs a zero current (in the latter case the measurement of switching is impossible). The LIM limit of this zone is not precisely determined, which is symbolized by the dashed vertical lines.

The determination of the position of the motor shaft is carried out by counting as long as the speed of the shaft (and therefore the switching frequency VFRQ) is greater than a first threshold TR1. As soon as the speed of the charge falls below this threshold, then the electromotive force is used: the velocity is obtained by determining the value of the electromotive force against and dividing it by the coefficient VKEMF. The integration of the speed gives the position of the motor shaft thus the position of the movable element.

In a simplified way, by taking a constant step of time to realize the algebraic sum Σ, the value VCNT stored in the counter CNT is worth:
VCNT = Σ (VEMF / VKEMF)

Thus, the counter CNT which reflects the position of the moving element therefore has two sources of incrementation and decrementation: the pulses from the comparator output C3 when the speed of the motor shaft is greater than the threshold speed TR1 and the integration of speed, calculated from the electromotive force when the speed of the motor shaft is less than the threshold speed TR1.

The coefficient VKEMF is calculated when the motor shaft has reached a speed TR2 which is preferentially greater than the speed threshold TR1: it is thus ensured that, when the coefficient VKEMF is calculated, the signal coming from the output C3 of the comparator has an equal frequency. the frequency of switching occurring between the brushes and the collector blades.

The coefficient VKEMF is:

VKEMF = VEMF / VFRQ with VEMF: value of the electromotive force stored in the memory EMF and VFRQ: value of the frequency of the signal coming from the output C3 stored in the memory FRQ.

VKEMF is then stored in a KEMF memory. This value of the electromotive force coefficient is therefore related to the engine temperature during the measurement, and corresponds to a value that is practically exact for the following time interval since the heating is not instantaneous.

An operating procedure of the actuator according to the invention is described with reference to FIG.

It is assumed that, in a first step 10, a user exerts an action on a command transmitter and that this action is interpreted by the actuator as an order to maneuver the mobile element so that it reaches a target position .

Following receipt of this order, in a step 20, the motor of the actuator is powered.

In a test step 30, the value VFRQ stored in the memory FRQ is tested.

If the value VFRQ stored in the memory FRQ is lower than the speed threshold TR1, proceed to step 50 in which, according to the direction of rotation of the motor, the counter CNT is incremented or decremented using the measurement of the force against electromotive motor. The VFRQ is below the speed threshold TR1 especially just after the start of the power supply of the motor due to the inertia of the rotor of the motor, the kinematic chain drive of the movable element and the movable element.

In a test step 60, the current value VCNT of the counter CNT is tested.

If the value VCNT is equal to the value V target corresponding to the target position of the moving element, the power supply of the motor is cut off in a step 70.

In the opposite case, the procedure loops on the test step 30.

If the value VFRQ stored in the memory FRQ is greater than the speed threshold TR1, proceed to step 40 in which, according to the direction of rotation of the motor, the counter CNT is incremented or decremented using the signal supplied by the output C3 of the comparator CMP. Following this step, the procedure continues with step 60 described above.

The process is susceptible of several variants.

For example, it is possible for the calculation of the electromotive force coefficient to be made at the moment when the speed of the motor rotor reaches the speed threshold TR1.

The threshold beyond which the voltage measurement ceases to be valid for the calculation of the position of the motor shaft and below which the voltage measurement is valid for the calculation of the position of the motor shaft can be a force threshold against electromotive. Indeed, at least over a range of speed values including the speed threshold TR1, the application giving the values of force against electromotive as a function of the speed values is bijective. Thus, at a value of force against electromotive corresponds a single rotor speed.

At the passage of the threshold, an action reducing the sensitivity of the switching detection device, such as in particular the startup "chopper" of the controlled switch, can be performed. In this case, the measurement of the electromotive force coefficient VKEMF is activated and the use of the electromotive force value for the calculation of the position of the rotor is validated before activating the "chopper" operation of the controlled switch.

The threshold value may be a threshold value of the intensity of the current flowing in the motor armature. Below a certain filtered value of the current, it is clear that the amplitude of the ripples of the unfiltered current becomes insufficient to detect switching and ensure the validity of the signal from the output C3 of the comparator CMP. In this case, a second comparator is used. On a first of its inputs is applied the URS voltage filtered by a low-pass circuit, while a reference voltage higher than the voltage URF is applied on his second entrance. The output of the second comparator is applied to a third input of the microcontroller.

More generally, the method according to the invention consists in preferentially using pulse counting as long as it is valid, and using the electromotive force in the opposite case. We take advantage of periods of validity of the count to update the value of the coefficient of electromotive force, which allows to better take into account the temperature of the engine.

In addition to the use of threshold values on the speed of the motor or, in an equivalent manner, on its electromotive force, it is possible to directly detect the validity of the counting of the pulses coming from the comparator CMP and corresponding to the commutations by analysis of the regularity. time of said pulses. Indeed, given the mechanical inertia of the moving assembly, it is impossible for the two time intervals separating three consecutive pulses to differ by a duration greater than a given time threshold value, unless an error of Switching detection does not occur.

This third threshold value, such as the first threshold value relating to the speed or the second threshold value relative to the electromotive force, is predetermined. In an alternative embodiment, they are calculated, for example in relative value. Thus, the first or second threshold value is a fraction of the largest value measured during a learning phase, while the third threshold value is a fraction of the lowest value measured during a learning phase. a learning phase. Such a calculation makes it possible to adapt the threshold to each type of engine and / or load.

Directly testing the validity of the pulse count by means of a time test makes it possible to immediately adapt to a situation where the parasites become numerous, for example because of the operation of the step-down chopper. However, it is also possible to declare the count invalid as soon as the chopper is activated, which avoids having to perform the time test.

• à réaliser la mesure du coefficient de force électromotrice et à stocker cette valeur VKEMF en mémoire,
• à passer en mode de mesure de la vitesse et/ou du déplacement de l'arbre moteur par mesure de la force contre électromotrice,
• à activer le hacheur.
  Pour simplifier la description précédente, on a décrit le stockage de valeurs de calcul dans des mémoires spécifiques. Il est clair pour l'homme du métier que seule la valeur du coefficient de force électromotrice du moteur doit être stockée en mémoire, entre deux remises à jour. Les autres valeurs comme la fréquence VFRQ ne sont mémorisées que pour autant qu'elles servent dans des calculs intermédiaires.

For example, a mode of execution of the method consists, when a phase of activation of the chopper must be engaged:

• to measure the electromotive force coefficient and to store this value VKEMF in memory,
• to switch to measuring mode of the speed and / or displacement of the motor shaft by measurement of the force against electromotive,
• to activate the chopper.
  To simplify the foregoing description, the storage of calculation values in specific memories has been described. It is clear to those skilled in the art that only the value of the electromotive force coefficient of the engine must be stored in memory, between two updates. Other values such as the VFRQ frequency are stored only as long as they are used in intermediate calculations.

The method makes it possible to measure the engine TETA temperature, without using an additional component. As seen previously, the coefficient VKEMF is directly related to the temperature of the magnets, an increase in temperature causing a decrease in the coefficient VKEMF. Then, either a mathematical function or a reading in a table, is used to obtain the value of the temperature TETA for a calculated value of the coefficient VKEMF.

Alternatively, the measurement of the temperature is obtained by using the value of the resistor RA of the armature, this value being calculated by dividing the difference (UM - EMF) by the current IM.

Claims (11)

Method for determining the position and / or the speed of the shaft of a DC motor (MOT) comprising an armature supplied via brushes and a blade commutator and for driving a movable element ( LD) of the building, characterized in that it comprises the following phases: - detect and count the commutations occurring between the brushes and the collector blades to determine the position and / or the speed of the motor shaft when the counting of the commutations is valid and - measure the electromotive force of the motor (MOT) to determine the position and / or the speed of the motor shaft when the counting of the commutations is not valid. Method according to claim 1, characterized in that the switching count is valid when the speed of the shaft is greater than a first threshold value. Method according to Claim 1, characterized in that the switching count is valid when the electromotive force of the motor is greater than a second threshold value. Method according to Claim 1, characterized in that the switching count is valid when the current flowing in the motor is greater than a third threshold value. Method according to Claim 1, characterized in that the counting of the switches is valid when the time difference between two time intervals measured between three commutations consecutive detected is less than a fourth threshold value. Method according to one of Claims 2 to 4, characterized in that the threshold value is predetermined. Method according to one of Claims 2 to 4, characterized in that the threshold value results from a calculation. Method according to one of the preceding claims, characterized in that , when the switching count is valid, the electromotive force against electromotive force coefficient (VKEMF) of the motor linking the electromotive force and the rotor speed is calculated and stored in a memory ( KEMF). Method according to one of the preceding claims, characterized in that the electromotive force against the motor is used to determine the motor temperature. Method according to Claim 8, characterized in that the engine temperature is obtained by using the motor electromotive force coefficient (VKEMF) value. Actuator (ACT) for operating a movable element (LD) of the building, comprising: a DC motor (MOT) having an armature supplied via brushes and a blade collector and means for counting the commutations between the brushes and the commutator blades, characterized in that it comprises means for measuring the electromotive force against the motor and means for inhibiting the the use of the switching counting means or the use of the motor electromotive force measurement means for calculating the position and / or the speed of the motor shaft.

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