阅读说明：本技术 用于确定转子的运动的方法 (Method for determining the movement of a rotor ) 是由 M·罗马斯泽克 G·维辛斯基 P·马伊 于 2020-04-10 设计创作，主要内容包括：本发明公开了一种用于确定转子的运动的方法。用于确定电动马达的转子的运动的方法包括：向电动马达的驱动线圈供应驱动信号；感测驱动线圈的线圈电流；检测由电动马达的转子跨过波纹产生位置而引起的感测到的线圈电流的电流波纹；从检测到的波纹推断出转子的运动；通过根据指定非零下降时间的制动曲线将供应给驱动线圈的驱动信号从初始信号值减小到零来制动马达,在所述非零下降时间期间,驱动信号从初始信号值减小到零,由此,调整制动曲线,使得在驱动信号已经减小到零之后,转子不会跨过波纹产生位置。(A method for determining motion of a rotor is disclosed. The method for determining the movement of the rotor of an electric motor comprises: supplying a driving signal to a driving coil of an electric motor; sensing a coil current of a driving coil; detecting a current ripple of the sensed coil current caused by the rotor of the electric motor crossing the ripple generating location; deducing the movement of the rotor from the detected ripples; braking the motor by reducing the drive signal supplied to the drive coils from an initial signal value to zero according to a braking profile specifying a non-zero fall time during which the drive signal is reduced from the initial signal value to zero, whereby the braking profile is adjusted such that the rotor does not cross the ripple generating location after the drive signal has been reduced to zero.)

1. A method (100) for determining a movement of a rotor of an electric motor (10), the method (100) comprising the steps of:

-supplying (105) a drive signal (50) to a drive coil of the electric motor (10),

-sensing (110) a coil current (42) of the drive coil,

-detecting (115) a current ripple of a sensed coil current (42) caused by the rotor of the electric motor (10) crossing a ripple generating position,

-deducing (120) a movement of the rotor from the detected ripples,

-braking the electric motor (10) by reducing the drive signal (50) supplied to the drive coil from an initial signal value (63) to zero according to a braking curve (60) specifying a non-zero fall time (65), during which non-zero fall time (65) the drive signal (50) is reduced from the initial signal value (63) to zero,

wherein the braking curve (60) is adjusted such that the rotor does not cross a ripple generating position after the drive signal (50) has been reduced to zero.

2. The method (100) of claim 1,

wherein the braking curve (60) is adjusted such that the coil current (42) does not reverse before the drive signal (50) has reached zero.

3. The method (100) according to any one of the preceding claims,

wherein the braking curve (60) causes the drive signal (50) to decrease linearly between the initial signal value (63) and a final signal value (64).

4. The method (100) of claim 3,

wherein the final signal value (64) is equal to zero.

5. The method (100) of claim 3,

wherein the final signal value (64) is not equal to zero,

wherein the braking profile (60) discontinuously drops the drive signal (50) from the final signal value (64) to zero.

6. The method (100) according to any one of the preceding claims,

wherein the drive signal (50) is controlled in accordance with the braking curve (60) using open loop control, in particular open loop control of a pulse width modulated control signal generating the drive signal.

7. The method (100) according to any one of the preceding claims,

wherein the drive signal (50) is adjusted according to the braking curve (60) using closed loop control, in particular using closed loop current control with the sensed coil current (42) as a feedback signal.

8. The method (100) according to any one of the preceding claims, the method (100) comprising the steps of:

-measuring (130) a measured initial coil current (42) before braking the electric motor (10),

-adjusting (135) a predetermined current curve (70), in particular adjusting the amplitude of the predetermined current curve (70), such that an initial value (72) of the predetermined current curve (70) matches the measured initial coil current (42),

-using (140) the adjusted predetermined current profile (70) as the braking profile (60) specifying the fall time (65).

9. The method (100) according to any one of the preceding claims,

wherein the fall time (65) of the braking curve (60) matches a predefined fall time (65) for all initial signal values (63), or

Wherein the slope of the braking curve (60) matches a predefined deceleration for all initial signal values (63).

10. The method (100) according to any one of the preceding claims, the method (100) comprising the steps of:

-receiving (125) a braking command for activating braking of the electric motor (10),

-determining (145) a phase of the electric motor (10),

-checking (147) whether the phase of the electric motor (10) reaches a predetermined phase after having received the braking command,

-starting to decrease (150) the drive signal (50) when the phase of the electric motor (10) reaches the predetermined phase.

11. The method (100) according to any one of the preceding claims,

wherein the electric motor (10) is a commutating electric motor (10), in particular a commutating brushed DC motor (10), wherein the corrugation generation position is a commutation position of the electric motor (10).

12. The method (100) according to any one of the preceding claims,

wherein the drive coil is an armature of the electric motor (10),

wherein the coil current (42) is an armature current of the electric motor (10).

13. A control system (30) for an electric motor (10), the control system (30) comprising:

a supply module (32), the supply module (32) being adapted to supply (105) a drive signal (50) to a drive coil of the electric motor (10);

a sensing module (34), the sensing module (34) adapted to sense (110) a coil current (42) of the drive coil;

a detection module (36), the detection module (36) being adapted to detect (115) a current ripple of a sensed coil current (42) caused by the rotor of the electric motor (10) crossing a ripple generating location, and to infer (120) a motion of the rotor from the detected ripple;

a control module (38), the control module (38) being adapted to brake the electric motor (10) by reducing the drive signal (50) supplied to the drive coil from an initial signal value (63) to zero according to a braking curve (60) specifying a non-zero fall time (65), during which non-zero fall time (65) the drive signal (50) is reduced from the initial signal value (63) to zero,

wherein the braking curve (60) is adjusted such that the rotor does not cross a ripple generating position after the drive signal (50) has been reduced to zero.

14. A vehicle having an electrically actuated drive for windows, sunroof, passenger seats, tailgate, etc., comprising an electric motor (10) and a control system (30) for the electric motor (10) according to claim 13.

Technical Field

The invention relates to a method for determining a movement of a rotor of an electric motor, a control system of an electric motor and a vehicle having an electrically actuated drive comprising an electric motor.

Background

Electrically actuated drives with electric motors are used in automotive applications to drive power windows, movable roofs, passenger seats, tailgate, etc. In low and medium power applications, these electric motors are typically configured as dc electric motors that are supplied with a dc drive signal and include a commutator to convert the drive signal into an ac drive signal having a phase and frequency that matches the position and speed of the electric motor. The alternating drive signal is fed to an electromagnetic drive coil of the electric motor, which constitutes the armature of the electric motor and interacts with a static magnetic field provided by the excitation structure of the motor (e.g. by an excitation winding or a permanent magnet). The armature may be positioned at the rotor or the stator of the electric motor.

In automotive applications, it is often desirable to detect the motion of the motor and infer, for example, the precise position and speed of the rotor. The movement of the motor may be detected by a dedicated sensor, such as a hall sensor. Alternatively, the movement of the motor can be inferred from current fluctuations of the drive signal (so-called current ripples caused by the moving rotor of the motor). These current ripples are caused, for example, by the commutator of the electric motor, which switches the phase of the drive signal, or may be caused when the magnetic field of the excitation structure interacting with the drive coil changes while the rotor is moving.

If the electric motor is configured as a Brushed Direct Current (BDC) motor, the commutator of the electric motor includes brushes that transmit drive signals to a commutation surface that, in turn, powers drive coils that generate magnetic fields to produce torque on the rotor of the electric motor. The commutator is linked to the rotor and as the rotor rotates, the brushes contact different sets of commutating surfaces. Most of the time, each brush contacts both diverting surfaces, but during each transition the brush only briefly contacts one diverting surface. During this transition, the current path changes and the internal resistance and inductance of the electric motor changes. This in turn varies the load represented by the motor and the current drawn by the motor. Repeated commutation then results in current ripple superimposed on the drive current. The number of waves per complete revolution of the rotor corresponds to the number of poles of the electric motor.

The position and speed of the rotor can be determined by detecting the current ripple of the coil current and counting it. In order to obtain an accurate position of the rotor, every ripple caused by the motion of the rotor should be detected and false counts caused by ripples that are not related to the motion of the rotor should be avoided.

Therefore, it is necessary to reliably detect the current ripple of the drive current of the electric motor associated with the movement of the rotor of the electric motor.

Disclosure of Invention

The present disclosure provides a method for determining a movement of a rotor of an electric motor, a control system of an electric motor and a vehicle having an electrically actuated drive comprising an electric motor. Embodiments are given in the dependent claims, the description and the drawings.

In one aspect, the present disclosure is directed to a method for determining motion of a rotor of an electric motor, the method comprising the steps of:

-supplying a drive signal to a drive coil of the electric motor,

-sensing a coil current of the drive coil,

-detecting a current ripple of a sensed coil current caused by the rotor of the electric motor crossing a ripple generating location,

deducing the movement of the rotor from the detected ripples,

-braking the motor by reducing the drive signal supplied to the drive coil from an initial signal value to zero according to a braking curve (breaking curve) specifying a non-zero fall time during which the drive signal is reduced from the initial signal value to zero,

thereby, the braking curve is adjusted such that the rotor does not cross the ripple generating position after the drive signal has decreased to zero.

By reducing the drive signal according to a braking profile specifying a non-zero fall time and by adjusting the braking profile so that the rotor does not cross the ripple producing position after the drive signal has been reduced to zero, all additional current that may cover the current ripple during braking is kept below a level above which the detection of the current ripple is prevented. These additional currents are, for example, induced currents caused by current changes in the drive coil during the reduction of the drive signal or currents generated by the rotation of the electric motor when the electric motor is decelerated (run down) to zero speed after the reduction or disconnection of the drive signal. Both the induced current and the current generated by the electric motor during deceleration are superimposed with the current ripple used to detect movement of the rotor, thereby increasing the likelihood of individual ripples being missed during detection or additional detection events occurring due to additional fluctuations in the additionally superimposed current.

The electric motor may be a direct current electric motor, in particular a commutated direct current electric motor (such as a commutated Brushed Direct Current (BDC) electric motor). The drive signal may be a unipolar drive signal and the commutated electric motor may comprise a commutator linked to the electric motor and converting the unipolar drive signal into at least two phase-shifted alternating electrical signals. The drive signal may be a pulse width modulated electrical signal generated by a current or voltage source connected to the drive coil.

The current ripple of the sensed coil current used to infer the motion of the rotor may be caused by the commutator changing phase, and the ripple-generating position of the electric motor may be a commutation position where the commutator switches phase. The current ripple may also be a fluctuation caused by a temporal change in the magnetic field generated in the drive coil by the excitation structure of the electric motor. Such excitation structure may be, for example, an excitation winding if the electric motor is a separately excited electric motor, or a permanent magnet if the electric motor is a permanently excited electric motor.

The current ripple may be detected by checking whether the modulation of the drive current reaches a predetermined value. The predetermined value may be an extreme value, such as a maximum or minimum value or a zero crossing of the modulated portion of the drive current. By high pass filtering the sensed coil current, the current ripple can be separated from the continuous portion of the sensed coil current.

The respective current ripple may trigger a counter when detected. The movement of the rotor can be inferred from the number of counted ripples (which yields the position of the rotor) and the frequency of the ripples or the time interval between individual ripples (which yields the speed of the rotor).

The drive signal supplied to the drive coil can be controlled by open loop control such that the drive signal directly follows the braking curve. The drive signal may also be controlled by closed loop control such that the drive signal is reduced in such a way that an additional controlled variable (e.g. the coil current flowing through the drive coil) follows the braking curve. The drive signal may for example be a pulse width modulated signal. When the drive signal is controlled by closed-loop control, the parameter used may be, for example, the duty cycle of the drive signal. The driving signal supplied to the driving coil may be generated by a supply module that is controlled by a control signal (e.g., a pulse width modulation control signal), and the supply module includes a transistor circuit that is switched by the control signal.

By adjusting the braking curve so that the rotor does not cross the ripple generating position after the drive signal has been reduced to zero, it is possible to avoid that the rotor crosses the ripple generating position when the coil current is determined entirely by the additional uncontrolled current generated during deceleration of the motor. This increases the accuracy of determining the movement of the electric motor, since the current generated during deceleration generally exhibits uncontrolled fluctuations which may overlap with the ripple actually used to detect the movement of the rotor.

In order to avoid the rotor crossing the ripple-generating position after reducing the drive signal to zero, the braking curve may be adjusted by having a negative slope and/or fall time that does not exceed a predetermined threshold above which additional crossing of the ripple-generating position may occur. Thus, the methods described herein may include additional steps for determining the negative slope and/or fall time of the braking curve for a particular electric motor. The braking curve may be characterized by portions having a constant negative slope, and there may be discontinuities between the portions having a constant negative slope. For example, the braking curve may include a single portion having a constant negative slope that begins at an initial signal value and extends to zero, or alternatively, extends to a final non-zero signal value and then abruptly drops to zero.

The negative slope and/or fall time of the braking curve may be determined experimentally by varying the negative slope and/or fall time of the braking curve and monitoring the movement of the rotor of a particular motor after reducing the drive signal to zero. All negative slope values and/or fall time values of the rotor across the ripple generating location after the drive signal has decreased to zero may be discarded. The negative slope and/or fall time of the braking curve can then be selected from the remaining values. The slope and fall time of the braking curve may be selected as the combination of the negative slope and the remaining value of the fall time which generally exhibits the shortest fall time. In this regard, it must be considered that the braking curve may include discontinuities such that the negative slope and the fall time may vary independently of each other.

The braking curve (in particular its negative slope and/or fall time) may be determined for a specific electric motor and may be stored in a memory unit of a control system executing the method. It is also possible to determine individual braking curves for a plurality of electric motors and to store all determined braking curves in the memory unit. The braking profile used during braking of the particular electric motor may then be selected from the stored braking profiles based on the electric motor actually connected to the controller. The control system may include, for example, a programming interface to receive a selection command specifying an electric motor connected to the controller.

The braking curve may be stored in the memory of the control system as a sequence of samples of the various values of the braking curve, the samples being spaced apart at fixed sampling intervals. The drive signal may be reduced stepwise at predetermined time intervals. The time interval may correspond to a sampling interval of samples of the braking curve stored in the storage unit. Additionally or alternatively, the time interval may be equal to a sampling interval of a detection algorithm for detecting a current ripple of the drive current. This minimizes the effect of the discrete reduction of the drive signal on the detection of current ripple.

According to one embodiment, the braking curve is adjusted such that the coil current does not reverse before the drive signal has reached zero. Similar to the uncontrolled current flowing in the drive coil after reducing the drive signal to zero, the reversal of the coil current may also mask the current ripple used to determine the motion of the rotor or may cause additional false fluctuations that lead to false detection events. The braking curve can be adjusted, for example by experimentally determining the negative slope and the fall time of the braking curve, such that it prevents the drive signal from reversing on the one hand and exhibits the shortest total fall time on the other hand.

According to one embodiment, the braking curve causes a linear decrease of the drive signal between the initial signal value and the final signal value. This enables the drive signal to be easily controlled during braking, especially when open-loop control of the drive signal is performed. The slope of the linearly decreasing braking curve may be adjusted to prevent the rotor of the electric motor from crossing the ripple generating location and/or to prevent the coil current from changing sign before the drive signal has reached zero.

According to one embodiment, the final signal value is equal to zero. This allows to continuously reduce the drive signal to zero and to avoid sudden and discontinuous drops of current fluctuations for determining the movement of the rotor that would disturb the drive signal.

According to an alternative embodiment, the final signal value is not equal to zero, whereby the braking curve causes the drive signal to drop discontinuously from the final signal value to zero. This allows for a short fall time. The final signal value may be adjusted to prevent crossing the ripple generation location after the drive signal has finally decreased to zero. For example, the final signal value may be adjusted to not exceed an experimentally determined maximum final signal value beyond which such crossing would occur. The maximum final signal value may depend on the negative slope of the drive signal during the linear decrease between the initial signal value and the final signal value.

According to one embodiment, the drive signal is controlled according to a braking profile using open loop control, in particular open loop control of a pulse width modulated control signal generating the drive signal. In this case, the braking profile may dictate the duty cycle of the pulse width modulated drive signal. During the fall time, the duty cycle may decrease linearly from the initial duty cycle value to the final duty cycle value, for example. The final duty cycle value may be zero or may be non-zero, for example. When a non-zero final duty cycle value is achieved, the duty cycle may suddenly drop to zero after the final duty cycle value has been reached.

According to an alternative embodiment, the drive signal is adjusted according to the braking profile using closed-loop control (in particular closed-loop current control with the sensed coil current as a feedback signal). In this case, the braking profile may specify a desired current profile according to which the sensed coil current is adjusted.

According to one embodiment, the method comprises the steps of:

-measuring the measured initial coil current before the brake motor,

adjusting the predetermined current profile, in particular the amplitude of the predetermined current profile, such that the initial value of the predetermined current profile matches the measured initial coil current,

-using the adjusted predetermined current profile as a braking profile for a specified fall time.

By measuring the initial coil current before braking the motor and by adjusting the predetermined current profile accordingly, the braking profile can be adapted to different load conditions of the motor. In automotive applications, the load experienced by an electric motor may depend on the amount of friction that occurs when the electric motor is moving an electrically actuated device (such as a power window, a movable roof, a tailgate, etc.). The friction may depend on the position of the device. For e.g. power windows, the friction depends on the size of the part of the window that is in contact with the rubber gasket surrounding the window in its closed position, so that during the final closing of the window the friction will increase.

According to one embodiment, the fall time of the braking curve matches a predefined fall time for all initial signal values. This allows the brake curve to be easily adjusted to different initial signal values, in particular when the brake curve is obtained from a predetermined brake curve stored in a memory unit of the control system executing the method. The braking curve can then be adjusted to a different initial signal value by scaling the amplitude of the braking curve to match the initial signal value.

According to an alternative embodiment, the slope of the braking curve is matched to the predefined deceleration for all initial signal values. This ensures that the additional current drawn by the brake motor is constant for all initial signal values and does not increase for higher initial signal values. Thus, when the drive current starts to decrease, all current ripples can be reliably detected regardless of the amount of drive current drawn by the motor.

According to one embodiment, the method comprises the steps of:

-receiving a braking command for activating braking of the motor,

-determining the phase of the electric motor,

-checking whether the phase of the electric motor reaches a predetermined phase after having received said braking command,

-starting to decrease the drive signal when the phase of the electric motor reaches a predetermined phase.

In other words, after receiving the braking command, the braking of the motor is delayed until the electric motor reaches a predetermined phase and the braking always starts at this predetermined phase. The predetermined phase may be selected in such a way that the rotor is prevented from crossing the ripple generating position after the drive signal has been reduced to zero according to the braking curve.

According to one embodiment, the electric motor is a commutating electric motor, in particular a commutating brushed dc electric motor, whereby the corrugation generating position is a commutation position of the electric motor. The number of ripple generating positions then corresponds to the number of phases of the electric motor.

According to one embodiment, the drive coil is an armature of an electric motor and the coil current is an armature current of the electric motor. The armature may be positioned at the rotor or the stator of the electric motor.

In another aspect, the present disclosure is directed to a control system for an electric motor, the control system comprising: a supply module adapted to supply a drive signal to a drive coil of an electric motor; a sensing module adapted to sense a coil current of a drive coil; a detection module adapted to detect current ripples of the sensed coil current caused by the rotor of the electric motor crossing a ripple generation position and to infer motion of the rotor from the detected ripples; and a control module adapted to brake the motor by controlling the supply module to reduce the drive signal supplied to the drive coil from an initial signal value to zero according to a braking profile specifying a non-zero fall time at which the drive signal is reduced from the initial value to zero. Thereby, the braking curve is adjusted such that the rotor does not cross the ripple generating position after the drive signal has decreased to zero.

The control system may be configured to perform the method of the present disclosure. In this connection, all the technical effects and embodiments described in connection with the method can also be applied to the control system mutatis mutandis.

The supply module may include a transistor circuit for generating a pulse width modulated drive signal, and the control module may be configured to generate a pulse width modulated control signal that is controlling the transistor circuit. The sensing module may be electrically connected to the driving coil to sense a coil current. For example, the sensing module may include a shunt resistor through which the coil current flows, and the sensing module may be configured to measure a voltage drop across the shunt resistor to determine the coil current. Instead of shunt resistors, the sensing module may comprise any other sensing means (e.g. flux gate, etc.). The control module may include a memory unit in which a brake curve or a predetermined current curve is stored. The control module may be configured to adjust a braking profile of the predetermined current profile to an initial signal value when the drive signal begins to decrease.

In another aspect, the invention is directed to a vehicle having an electrically actuated drive for a window, a movable roof, a passenger seat, a tailgate, etc., comprising an electric motor according to the present disclosure and a control system for the electric motor. All the technical effects and embodiments of the control system and of the electric motor described in connection with the method and control system of the present disclosure can also be applied, mutatis mutandis, to the actuating drive of the vehicle. For example, the electric motor may be configured as described in connection with the methods and control systems of the present disclosure. The electric motor may be, for example, a commutated brushed dc motor, and the ripple generating position is a commutation position of the electric motor.

Drawings

Exemplary embodiments and functions of the present disclosure are described herein in connection with the following figures, which are schematically illustrated:

FIG. 1 shows a first embodiment of an electrically actuated drive;

fig. 2 shows the time dependence of the coil current of an electric motor when the drive signal is suddenly switched off according to the prior art;

FIG. 3 shows an enlarged view of a portion of the time dependent coil current shown in FIG. 2;

FIG. 4 illustrates a braking curve according to the present disclosure;

FIG. 5 shows the time dependence of the coil current during the reduction of the drive signal according to the braking curve;

FIG. 6 shows the time dependence of the coil current for a braking curve with non-optimal fall time and slope;

FIG. 7 shows the time dependence of the coil current for a braking curve with a suitably adjusted fall time and slope;

FIG. 8 shows the time dependence of the coil current for another braking curve with a non-optimal fall time and slope;

FIG. 9 shows the time dependence of the coil current for another braking curve with a non-optimal fall time and slope;

FIG. 10 shows the time dependence of the coil current for another braking curve with a non-optimal fall time and slope;

FIG. 11 shows the time dependence of the coil current for another braking curve with a non-optimal fall time and slope;

FIG. 12 shows a second embodiment of an electrically actuated driver;

FIG. 13 illustrates a predetermined current profile for generating a braking profile for closed loop control;

FIG. 14 illustrates a closed loop reduction of the drive signal according to a braking curve;

FIG. 15 illustrates a method for closed loop control performed by the control module;

fig. 16 shows a method for determining the movement of the rotor of an electric motor.

List of reference numerals

1 electrically actuated drive

5 region

10 electric motor

30 control system

32 supply module

34 sensing module

36 detection module

38 control module

39 brake control module

40 memory cell

42 coil current

43 average coil current

44 coil voltage

46 wave

50 drive signal

52 supply voltage

54 control commands

56 control signal

58 crossing event

60 desired braking curve

Time 61

63 initial signal value

64 final signal value

65 fall time

66 onset of signal reduction

67 end of signal reduction

69 switching time

70 predetermined current curve

72 initial value

100 method

101 method

102 start

105 supplying a drive signal

107 checks whether the motor is running

108 do not run

109 run

110 sense coil current

115 sense current ripple

120 inferring motion of the rotor

122 determine an average coil current

125 receive brake commands

127 checking braking

128 without braking

129 brake

130 measure the measured initial coil current

135 adjusting the predetermined current curve

140 use the adjusted predetermined current profile as a braking profile

145 determines the phase of the electric motor

147 inspection

150 reducing the drive signal

152 stop of inspection

153 have not stopped

154 stopping

170 end of

Detailed Description

Fig. 1 depicts a first embodiment of an electrically actuated drive 1, which electrically actuated drive 1 comprises an electric motor 10 and a control system 30. The electric motor 10 is configured as a commutating brushless dc motor. The control system 30 comprises a supply module 32, which supply module 32 is connected to a drive coil of the electric motor 10 and supplies a drive signal 50 to the drive coil. The control system 30 also includes a sensing module 34, the sensing module 34 also being connected to the drive coil of the electric motor 10 and configured to sense a coil current 42 flowing through the drive coil. The detection module 36 of the control system 30 is connected to the sensing module 34 and detects a current ripple of the sensed coil current 42 that is generated when the rotor of the electric motor 10 crosses the ripple generation position. The detection module 36 is also configured to infer a movement of the rotor of the electric motor 10 from the detected ripple.

The control system 30 also includes a control module 38, the control module 38 being connected to the supply module 32 and providing a Pulse Width Modulation (PWM) control signal 56 to the supply module 32. Based on the control signal 56, the supply module 32 generates the drive signal 50 as a pulse width modulated signal from the supply voltage 52. The control module 38 is configured for open loop control of the drive signal 50. When the motor 10 is de-energized or braked, the control module 38 decreases the drive signal 50 according to a braking curve 60 stored in the memory unit 40 of the control system 30. The braking curve 60 constitutes a desired braking curve 60, which desired braking curve 60 is used as a reference signal for the brake motor 10.

Fig. 2 depicts the time dependence of the sensed coil current 42 when the drive signal 50 is abruptly reduced at a switching time 69 without employing the braking curve 60. In this case, the coil current 42 exhibits a large current spike when the electric motor 10 decelerates to zero speed after turning off the drive signal 50. Further, since the electric motor 10 functions as a generator when decelerating without applying the drive signal 50, the direction of the coil current 42 is reversed during deceleration of the electric motor 10.

Fig. 3 depicts an enlarged view of the area bounded by box 5 of fig. 2. The sensed coil current 42 exhibits a current ripple 46 that has a high signal-to-noise ratio and is therefore reliably detectable whenever the drive signal 50 is applied to the drive coil. The current ripple 46 is generated at a cross event 58 where the rotor of the electric motor 10 crosses the ripple generation location. As can be seen from the step-over event 58 depicted in fig. 3, the electric motor 10 steps over the ripple generation position nine times after the drive signal 50 has been turned off at the switching time 69. However, the current ripples 46 associated with the nine ride-through events 58 are superimposed by large current spikes caused by turning off the drive signal 50, such that these current ripples 46 may not be reliably detected. This leads to errors when the movement of the rotor and the rotor position are derived by counting the detected current ripples 46.

By reducing the drive signal 50 according to the braking curve 60 when the electric motor 10 is switched off or braking, the current spikes depicted in fig. 2 and 3 can be avoided. Accordingly, the control module 38 decreases the drive signal 50 over time 61 according to the braking curve 60, as shown in FIG. 4. As can be seen, the control module 38 varies the duty cycle of the pulse width modulated control signal 56 in accordance with the braking curve 60 such that the drive signal 50 varies linearly during a fall time 65 from an initial signal value 63 at a beginning 66 of the reduction of the drive signal 50 to a final signal value 64 at an end 67 of the reduction of the drive signal 50. When the final signal value 64 is reached at the end 67 of the fall time 65, the drive signal suddenly falls to zero. In addition to the duration of the fall time 65, the braking curve 60 is also characterized by a linear decrease in the slope of the drive signal 50 during the fall time 65. The slope is given by the difference of the initial signal value 63 and the final signal value 64 divided by the fall time 65.

Fig. 5 depicts the effect of reducing the drive current 50 according to the braking curve 60 depicted in fig. 4. The coil current 42 gradually decreases to zero and during the reduction of the drive current 50 the current ripple 46 remains clearly visible and detectable. As can be inferred from the crossing event 58 depicted in fig. 5, the fall time 65 and the slope of the brake curve 60 are selected in such a way that the rotor of the electric motor 10 does not cross the ripple generating position after switching off the drive signal 50 at the end 67 of the reduction of the drive signal 50. Thus, there is no ripple 46 that may be masked by residual current spikes generated after the drive signal 50 is turned off.

Fig. 6 depicts the time dependence of the coil current 42 for a braking curve 60 having a non-optimal fall time 65 and slope. The braking curve 60 exhibits the same slope as the braking curve shown in fig. 5, but with a shorter fall time 65. This can result in a premature disconnection of the drive signal 50, causing the rotor to cross the additional ripple generation location after the end 67 of the reduction of the drive signal 50. Thus, the corresponding ripple 46 is masked by current spikes generated during deceleration of the motor 10 and may be missed during detection.

Fig. 7 depicts the time dependence of the coil current 42 for another braking curve 60 with a suitably adjusted fall time 65 and slope. Again, after the end 67 of the reduction of the drive signal 50 to zero, the rotor does not cross the ripple generation position. In addition, at the end 67 of the reduction of the drive signal 50, the coil current 42 does not reverse until the drive signal 50 has reached zero. Thus, all ripples exhibit a high signal-to-noise ratio, and thus they can be reliably detected.

Fig. 8 depicts the time dependence of the coil current 42 for another braking curve 60 having a non-optimal fall time 65 and slope. The other braking curve 60 depicted in fig. 8 exhibits the same fall time 65, but a steeper slope, and the drive signal 50 falls linearly to zero as compared to the braking curve 60 shown in fig. 7. The steeper slope of the braking curve 60 depicted in fig. 8 causes the coil current 42 to change sign before the drive signal 50 has reached zero at the end 67 of the decrease in the drive signal 50. This results in additional spurious ripple of the coil current 42 that triggers the detection module 36 to falsify the position of the rotor derived from the current ripple 46.

Fig. 9 depicts the time dependence of the coil current 42 for another braking curve 60 having a non-optimal fall time 65 and slope. The other braking curve 60 depicted in fig. 9 exhibits the same fall time 65, but a more gradual slope, as compared to the braking curve 60 shown in fig. 7. This results in a larger final signal value 64 and, therefore, a larger current spike of the coil current 42 when switching from the larger final signal value 64 to zero. As a result, the rotor of the electric motor 10 crosses the ripple generation position after the end 67 of the reduction of the drive signal 50, and the corresponding ripple is masked by the current spike generated in the drive coil.

Fig. 10 depicts the time dependence of the coil current 42 for another braking curve 60 having a non-optimal fall time 65 and slope. The further braking curve 60 depicted in fig. 10 exhibits a shorter fall time 65 and a steeper slope compared to the braking curve 60 shown in fig. 7, while its final signal value 64 corresponds to the final signal value 64 of the braking curve 60 shown in fig. 7. As a result, the coil current 42 reverses before the drive signal 50 is turned off at the end 67 of the reduction of the drive signal 50. In addition, after the drive signal 50 is turned off, the rotor crosses the ripple generating position.

Fig. 11 depicts the time dependence of the coil current 42 for another braking curve 60 having a non-optimal fall time 65 and slope. The further braking curve 60 depicted in fig. 11 exhibits a more gradual slope and a longer fall time 65 compared to the braking curve 60 shown in fig. 7, while its final signal value 64 corresponds to the final signal value 64 of the braking curve 60 shown in fig. 7. Although the rotor does not cross the ripple generation location and the coil current 42 does not reverse after the drive signal 50 is turned off, it can be concluded by comparing the braking curves 60 shown in fig. 7 and 11 that the braking curve 60 of fig. 11 results in a longer fall time 65 than is required to ensure reliable detection of all current ripples 46 caused by the rotor of the electric motor 10.

Fig. 12 depicts a second embodiment of an electrically actuated drive 1 for enabling closed-loop control of a drive signal 50 supplied to an electric motor 10. The electrically actuated driver 1 according to the second embodiment comprises a supply module 32 for supplying a drive signal 50 to a drive coil of the electric motor 10, a sensing module 34 for sensing a coil current 42 of the motor 10 and a detection module 36. The supply module 32 receives a supply voltage 52 and a control command 54 that controls the direction of movement of the electric motor 10.

The electrically actuated driver 1 shown in fig. 12 includes a second embodiment of the control module 38 described herein. According to a second embodiment, the control module is configured to perform closed-loop control of the drive signal 50 by communicating the control signal 56 to the supply module 32 to control the drive signal 50 generated by the supply module 32. For closed loop control, a coil voltage 44 representing the voltage applied to the drive coils of the electric motor 10 and a coil current 42 sensed by the sensing module 34 are fed back to the control module 38. The control module 38 controls the drive signal 50 in such a way that the sensed coil current 42 follows a braking curve 60 supplied to the control module 38 by the brake control module 39.

The braking control module 39 is configured to adjust the predetermined current curve 70 stored in the memory unit 40 of the control system 30 such that the initial value of the predetermined current curve 70 matches the measured initial coil current 42 at the beginning of braking of the motor 10. This measured initial coil current 42 is measured before braking the motor 10. For example, the measured initial coil current 42 may represent an average coil current 42 flowing through the drive coils at the beginning of the decrease in the drive signal 50 during braking.

Fig. 13 depicts a predetermined current curve 70 for generating the braking curve 60, according to which predetermined current curve 70 the control module 38 reduces the drive signal 50 to zero. The predetermined current curve 70 continuously decreases from an initial value 72 at the start 66 of the decrease of the drive signal 50 to zero at the end 67 of the decrease of the drive signal 50. The predetermined current profile 70 may be analytically specified by a mathematical formula stored in the memory unit 40 and evaluated by the brake control module 39. Alternatively, samples of the predetermined current curve 70 may be stored in the storage unit 40. The samples may be spaced apart by a fixed sampling interval. The sampling interval may correspond to the sampling interval of the detection algorithm employed by the detection module 36 to detect the current ripple used to infer movement of the rotor of the electric motor 10. This minimizes the effect of the discrete reduction of the drive signal 50 on the detection of current ripple.

Fig. 14 depicts the effect of reducing the drive signal 50 according to the braking curve 60 by using closed loop control of the control system 30 according to the second embodiment. It can be seen that the average value 43 of the coil current 42 closely follows the braking curve 60 derived from the predetermined current curve 70. The braking curve 60 has been generated by adjusting the amplitude of the predetermined current curve 70 such that the initial value 72 of the predetermined current curve 70 matches the average value 43 of the sensed coil current 42 at the beginning of the decrease of the drive signal.

FIG. 15 depicts a method 101 performed by the control module 38 and the brake control module 39 to reduce the drive signal 50 according to the braking curve 60. After the start (102), the method comprises checking 107 whether the motor 10 is running. The check 107 is repeated as long as the motor 10 is not running (108). If the motor 10 is running (109), an average value 43(122) of the coil current 42 is determined and it is checked (127) whether the motor 10 is braking. The braking of the motor 10 may be inferred from a braking command received by the control module 38, for example from a stop button or a main control unit, or may be inferred from a decrease in the average value 43 of the coil current 42. As long as the motor is not braking (128), the determination 127 of the average 43 and the check 127 of whether the motor is braking are repeated.

If the motor is braking (129), the measured initial coil current 42 is determined (130) by reading the actual average value 43 of the coil current 42 determined in step 122 as the measured initial coil current 42 for adjusting the predetermined current curve 70. Subsequently, the method 101 comprises adjusting 135 the amplitude of the predetermined current curve 70 such that the initial value 72 of the predetermined current curve 70 corresponds to the average value 43 of the measured initial coil current 42. The drive signal 50 is then reduced (150) according to the braking curve 60 given by the adjusted predetermined current curve 70. After the drive signal 50 is reduced 150, it is checked 152 whether the motor 10 is stopped (stand). The reduction 150 of the drive signal 50 is repeated as long as the motor 10 is not stopped (153). When the motor 10 is stopped 154, the method ends 170.

In general, the electrically actuated drive 1 performs the method 100 depicted in fig. 16 for determining the motion of the rotor of the electric motor 10. After the start (102), the method 100 comprises supplying 105 a drive signal 52 to a drive coil of the electric motor 10. The method 100 further includes sensing 110 the coil current 42, detecting 115 a current ripple of the coil current 42, and inferring 120 motion of a rotor of the electric motor 10 from the current ripple. The method 100 may also include inferring rotor position from the current ripple. After receiving 125 the brake command, the method 100 includes measuring 130 the measured initial coil current 42 and adjusting the magnitude of the predetermined brake curve 70 such that the initial value 72 of the predetermined current curve 70 matches the measured initial coil current 42. The adjusted predetermined braking curve 70 is then used (140) as the braking curve 60, according to which braking curve 60 the drive signal 50 will be reduced.

Method 100 also includes determining 145 a phase of electric motor 10 after receiving 125 a braking command. Then, it is checked (147) whether the phase of the electric motor 10 reaches a predetermined phase and, once the electric motor 10 reaches this predetermined phase, the drive signal 50 is reduced (150) according to the braking curve 60. When the drive signal 50 has decreased to zero, the method ends (170).