The present invention relates to a position control device for motors and to an associated method. The system according to the present invention makes no use of position sensors, e.g. Hall effect ones, in order to determine the position of the rotor of a motor; such a system is referred to as "sensorless" .

Said system is applicable to electric motors, preferably to commutator-type DC motors, e.g. equipped with a laminated commutator.

The system and the method according to the present invention are preferably applicable for controlling the position of the rotor of at least one motor adapted to move a seat sliding on movable slides, in particular for moving it in all possible directions.

One typical seat moving application is found in the automotive field, particularly in medium/high-range cars.

Such cars, in fact, utilize electronic actuators, such as motors, for seat adjustment purposes. Said seats may also include a system for storing seat positions for different drivers.

In general, this control can be employed in any installation making use of electric motors, e.g. commutator-type DC motors, particularly wherever it might be necessary to eliminate the position sensor.

In the above-mentioned automotive applications, there is a need for reducing the costs incurred for moving said seats. The prior art has tried to solve this problem by using actuators with sensorless control to determine the rotor position. Such a typology of control systems allows to eliminate Hall-effect sensors, which are normally associated with the motor for determining the rotor position, resulting in lower implementation costs. In fact, the use of this type of sensor requires the provision of a complex electric wiring to be integrated into the seat, thus increasing the seat production costs.

More in particular, control systems are known which comprise a microcontroller adapted to acquire electric quantities, such as voltage and current, in the motor windings and to process algorithms based on mathematical models and/or numerical observers for the purpose of determining the angular position of the rotor.

This solution is very complex in terms of algorithm computation, requiring also very accurate measurements with reduced uncertainty. Moreover, the error that may be associated with the rotor position result thus obtained is very large and depends on secondary application conditions such as, for example, environmental temperature variations or the presence of electromagnetic noise in the vicinity. Such a solution, therefore, does not allow to reduce the uncertainty in the actual angular position of the rotor of the motor, because the algorithm that regulates the system has very high intrinsic uncertainty.

A seat position control system is also known from patent application DE102006015920. Said system comprises a brush-type electric motor and a control device, which processes the electric signals in order to determine the position of the motor. Patent application WO10009705 discloses a brush-type DC motor equipped with a commutator with peripherally arranged laminates. The brushes rubbing against said laminates are adapted to supply current to the windings and to receive the ripple currents generated by the same windings .

The present invention aims at solving the above technical problems by providing a control system and an associated method for detecting the angular position of the rotor of a motor.

One aspect of the present invention relates to a control system for motors having the features set out in the appended independent claim 1.

A further aspect of the present invention relates to a control method for motors having the features set out in the appended independent claim 10.

Auxiliary features are set out in corresponding dependent claims.

The features and advantages of the control system and of the associated control method according to the present invention will become more apparent from the following description of different non-limiting embodiments thereof and from the annexed drawings, wherein:

• Figures 1A, IB show block diagrams of the control system according to the present invention when applied to a motor; in particular, Figure 1A shows the system in its minimal configuration, whereas Figure IB shows a system comprising a processing device for specific motor applications;

· Figures 2A and 2B show two embodiments of the system of Figure IB; in particular, Figure 2A shows the system adapted to measure a current and to calculate the first derivative thereof, whereas Figure 2B shows the system adapted to measure a voltage and to calculate the first derivative thereof;

· Figures 3A, 3B show alternative embodiments of the control system according to the present invention; in particular, Figure 3A comprises multiple measuring circuits, wherein derivatives of a higher order than the first-order derivative are calculated for each electric quantity measured, whereas Figure 3B also comprises a plurality of processing devices 32;

• Figure 4 shows in detail the control system according to the present invention, which comprises a plurality of measuring circuits and wherein, for each electric quantity measured, a plurality of time derivatives are calculated and processed by a single processing device;

• Figure 5 shows a flow chart of a non-limiting embodiment of the control method according to the present invention .

With reference to the above-mentioned drawings, control system 3 is adapted to determine the position of a motor 1, e.g. an electric motor, preferably a DC motor.

The motor comprises a rotor 11, which in turn comprises a shaft 12 to which a commutator 13 is fitted.

At least two brushes 14 are associated with and rub against said commutator 13. Said brushes 14, preferably in a number of two or a multiple thereof, are adapted to induce current towards the windings of rotor 11 when a power supply circuit 15 of said motor 1 is activated.

Commutator 13 comprises a plurality of laminates 131 arranged radially, each one being preferably located in a cavity of the windings of rotor 11, for the purpose of creating a substantially circular commutator structure.

For the purposes of the present invention, the term "substantially circular commutator" means that the number and shape of laminates 131 is such as to create a commutator whose outer perimeter describes a circumference, as shown by way of example in Figures 1A, IB, 2A, 2B, 3A and 3B.

Said system 3 is operationally connected to said power supply circuit 15 of said motor 1.

System 3 comprises at least one measuring circuit 30 adapted to measure at least one electric quantity generated by said power supply circuit.

System 3 according to the present invention comprises at least one differentiator circuit 31, which is adapted to calculate at least one time-derivative of at least one electric quantity measured by said at least one measuring circuit 30.

Said differentiator circuit 31 outputs an electric signal which is a function of the relative angular position of motor 11, as shown in Figure 1A.

System 3 preferably comprises at least one processing device 32, which is adapted to process the electric signal outputted by said at least one differentiator circuit 31 for the purpose of determining the angular position of rotor 11 relative to a predetermined position, as shown by way of example in Figure IB.

In the embodiment shown in Figure 2A, the system according to the present invention comprises a measuring circuit 30 for measuring at least one fraction of the current flowing through the windings of rotor 11, applied by means of said brushes 14.

Preferably, said measuring circuit 30 is a shunt, e.g. a resistive shunt.

The shunt must have predetermined technical characteristics, in particular a resistance value with reduced uncertainty and high thermal capacity, in order to limit temperature-dependent resistance value variations.

In an alternative embodiment, measuring circuit 30 is a magmatic flow sensor, adapted to detect the magnetic field generated by at least one current flowing through a conductor located in the proximity of the measuring circuit 30, e.g. the tracks or wires that supply power to said brushes 14.

Said measuring circuit 30 is preferably implemented through closed- loop current sensors, based on magnetic flow probes .

In the present embodiment, the measuring circuit thus designed will return a voltage proportional to the current flowing in brushes 14.

In alternative embodiments, such as the one shown in Figure 2B, said measuring circuit 30 is adapted to measure a voltage across brushes 14.

In the embodiments shown in Figures 3A, 3B and 4, control system 3 according to the present invention comprises a plurality of measuring circuits 30, each one adapted to measure a different electric quantity, such as voltage, current, etc., at the same time instant.

Said differentiator circuit 31 is preferably adapted to calculate the first derivative in the time domain of at least one electric quantity measured by said at least one measuring circuit 30.

In the preferred embodiment, differentiator circuit 31 is a capacitive differentiator circuit, more preferably an active differentiator.

In the embodiment shown in Figures 2A and 2B, differentiator circuit 31 is adapted to calculate the first derivative of the measured electric quantity.

More in detail, in Figure 2A differentiator circuit 31 is adapted to calculate the first derivative of the current measured by measuring circuit 30, whereas in Figure 2B differentiator circuit 31 is adapted to calculate the first derivative of the voltage measured by measuring circuit 3.

In alternative embodiments, for example as shown in Figures 3A and 3B, differentiator circuit 31 is adapted to calculate the second derivative, in the time domain, of at least one electric quantity measured by said at least one measuring circuit 30.

More in detail, in the embodiment shown in Figures 3A and 3B there are two differentiator circuits 31 arranged in cascade, each one adapted to calculate the time derivative of the electric quantity measured by said at least one measuring circuit 30.

Derivatives of a higher order than the second one may possibly be calculated, by arranging in cascade several differentiator circuits 31, e.g. adapted to calculate the first derivative.

In alternative embodiments not shown in detail herein, it is possible to use a single monolithic differentiator circuit adapted to return a plurality of derivatives of one or more input signals. Such a differentiator may be implemented, for example, by means of FPGA circuits.

The output signal of said differentiator circuit 31 returns a signal which is a function of the relative position of rotor 11 of a motor 1, to which system 3 according to the present invention is applied.

Said at least one processing device 32 is adapted to determine the angle of rotation of rotor 11 relative to a predetermined position, depending on the specific application of motor 1.

Preferably, the predetermined position is that position in which rotor 11 was located at the instant when the power supply circuit 15 began supplying power to the same motor 1.

Said processing device 32 is, for example, a microprocessor adapted to process said electric signals outputted by said at least one differentiator circuit 31.

In an embodiment not shown in the drawings, said processing device 32 may also receive, in addition to electric signals outputted by said at least one differentiator circuit, the electric signals outputted by said at least one measuring circuit.

Said processing device 32 can process said electric signals in real time. Processing device 32 may also be able to process said received electric signals a posteriori , and to send the processing results, e.g. as data, to a centralized control unit.

Said centralized control unit may then further process said data and use them, for example, for providing an indication to the user, e.g. through a graphic interface. In the preferred embodiment, processing device 32, which is adapted to process the data received from said at least one differentiator circuit 31, comprises a counter for determining the angle, i.e. the relative angle or the absolute angle, of rotor 11.

More in detail, the counter can count predetermined electric events inputted to processing device 32, e.g. the crossing of a predetermined threshold.

Said counter can, for example, count the electric pulses obtained from the differentiation of an electric quantity applied to brushes 14.

In the preferred embodiment, processing device 32 is adapted to detect an electric pulse or the achievement of a predetermined threshold of an electric signal. Said processing device 32 can, through said counter, count the number of pulses or threshold achievements, and can consequently determine the angular position of rotor 11.

More in detail, in the embodiment shown in Figure 2A the supply current measured by measuring circuit 30 has a substantially square-wave profile.

For the purposes of the present invention, the expression "substantially square-wave signal" refers to a time-periodic signal switching between two logic levels or states (in the present case taking current into account) , wherein the time required for switching between the two logic levels or states is substantially negligible, e.g. shorter than 1/100 of the signal period.

More in detail, the period of the square-wave signal represents a fraction of the revolution speed of rotor 11. Furthermore, the period of the square-wave signal is a function of the number of laminates 131 present on commutator 13.

The first derivative in the time domain of a square- wave signal consists of electric pulses at the switching instants, which are positive when switching to the high logic state (higher current) or negative when switching to the low logic state (lower current) .

The possible additional derivative of such electric pulses (in the present case taking current into account) , corresponds to a pulse which has an even shorter duration but is more intense, since its switching edges are very- steep. The single pulse generated by differentiating the measured signal is a function of the passing of brush 14 over two successive laminates 131. Since the number of laminates 131 of commutator 13 is finite, the differentiated signal outputted by differentiator circuit 31 has a number of pulses which is directly proportional to the angle of rotor 11.

The processing circuit is therefore capable of counting at least the positive pulses generated by differentiation which correspond to brush 14 passing over two successive laminates 131. Since the number of laminates 131 of commutator 13 is finite, the number of counted pulses is proportional to the angle of rotor 11.

Knowing the number of laminates 131 present in commutator 13, it is possible, through the number of detected pulses, to determine the variation in the angle of the rotor with respect to a predetermined point, e.g. the point where the rotor was at when motor 1 was turned on. For the embodiment shown in Figure 2B, the voltage measured across the brushes has a profile substantially equal to a sen ² (rot) function.

The first derivative of a sen ² (rot) function is 2*sen (rot) *cos (rot) with double pulsing of the sen ² (rot) signal.

The zero-crossings of the differentiated signal substantially correspond to the instants when the brush is between two laminates 131 and when it is at the centre of one laminate 131. The profile of said signal is a function of the angle of rotor 11.

By detecting the zero-crossings it is possible to determine the instants when the brush is between two laminates 131 and when it is at the centre of one laminate 131.

By processing data outputted by said one or more differentiator circuits 31, one can obtain different and increasingly accurate information about the angular position of rotor 11. In the embodiments shown in Figures 3B and 4, said at least one processing device 32 receives at least one signal corresponding to the first derivative of the measured electric quantity, and one signal corresponding to the second derivative of the same electric quantity, aiming at reducing the uncertainty of the position of rotor 11.

By combining the circuit illustrated in Figures 2A and 2B, as shown by way of example in Figures 3A and 3B, and by calculating the current and voltage derivative of at least the first order, it is possible to reduce the uncertainty of the position of rotor 11. The uncertainty of the position of rotor 11 can be further reduced by increasing the number of laminates 131 of commutator 13.

The system according to the present invention is preferably applicable to a car seat comprising a motor for moving the seat itself.

System 3 is also applicable to a motor for moving the windscreen wipers of a vehicle or a boat.

System 3 according to the present invention may be included in a motor 1.

Processing device 32 may possibly comprise a non-volatile memory or may be connected to a storage circuit, into which the points where motor 1 is stopped are saved in order to be able to know the absolute movement of motor 1, e.g. relative to a preset initial point, such as an end-of-travel position of the seat whereto said system has been applied. This latter solution allows determining the absolute position of the seat, not only its position relative to the position where the motor was turned on.

The method for controlling the position of a motor 1, associated with the above system, comprises the following steps :

a) measuring at least one electric quantity generated by at least one power supply circuit 15 of said motor;

b) calculating at least one derivative of at least one electric quantity measured in the preceding step.

After step b) of calculating at least one derivative, there is preferably a step c) of processing said at least one derivative, calculated in the preceding step, for the purpose of determining the position of a rotor 11 relative to a predetermined position.

As shown by way of example in Figure 5, prior to the measuring step a) there is an additional step aO) of verifying the activation of motor 1.

During said step aO) , it is verified whether the motor is active or not, e.g. by checking if there is current and/or voltage across brushes 14.

Step a) of measuring at least one electric quantity is preferably carried out continuously over time, e.g. when power supply circuit 15 is active.

The measuring step a) may be carried out in parallel through a plurality of measuring circuits 30 adapted to measure the same electric quantities or different electric quantities, such as current, voltage, etc.

Step b) of calculating at least one derivative is also carried out in real time and continuously over time, by differentiating the electric signal measured in the preceding step a) . Said step is carried out in order to determine the relative angular position of rotor 11.

The first time-derivative in the time domain of the signal measured in the preceding step a) is preferably calculated. It is also possible to calculate time- derivatives of a higher order than the first one. In order to calculate derivatives of higher orders, one can arrange in cascade two or more differentiator circuits, e.g. of the first order.

The processing step c) can process the data obtained in the preceding differentiating step b) , for the purpose of determining the angular position of rotor 11, e.g. depending on the specific application of system 3. More in detail, it is possible to process at the same time data deriving from different differentiation orders, e.g. the first and second orders, and even relating to distinct physical quantities, such as currents and voltages.

Preferably, as shown in Figure 5, after step c) there is a verification step d) . In the verification step d) it is verified if motor 1 is still active.

The method according to the present invention repeats steps a) -c9 until, during step d) , it is detected that motor 1 has stopped. Preferably, the present method stops when motor 1 is turned off.

The currents used in motors for automotive applications, in particular for electrically adjustable seats, may reach typical values of 30A rms .

The system according to the present invention represents an electronic solution for detecting the relative position of rotor 11 of a motor 1, preferably a commutator- type DC motor. The system according to the present invention turns out to be more reliable and more robust to operating conditions, and does not require the use of a microcontroller providing high computational performance, thus not being affected by the problems suffered by the prior art.

The solution to the above-mentioned problems is thus achieved through a solution that uses a H circuit for determining the rotor position and for processing at least one electric quantity, e.g. the commutator current of motor 1, in particular for executing at least one differentiation operation on said signal, e.g. of the first order. The different embodiments described herein should not be considered to limit the scope of the invention.

REFERENCE NUMERALS

Motor 1

Rotor 11

Shaft 12

Commutator 13

Laminates 131

Brushes 14

Power supply circuit 15

Control system 3

Measuring circuit 30

Differentiator circuit 31

Processing device 32