Position sensor and method for redundantly determining a position

Abstract

A position sensor for redundantly determining the position of an element (10) that is movable by a drive motor (20), comprising a primary sensor (110) and a secondary sensor (120). The primary sensor (110) is designed to directly sense the position of the movable element (10). The secondary sensor (120) is designed to derive the position of the movable element (10) from at least one secondary measurement (25), wherein the secondary measurement (25) is based on a drive variable of the drive motor (20).

Description

The present invention relates to a position sensor and method for redundantly determining a position, and more particularly to hybrid strategies for control of redundant electric motors in safety-critical applications, based on sensory and sensorless control.In particular in safety-critical applications, redundant detection or determination of a motor position is of great importance in order to be able to continue to determine motor positions even in the event of a sensor failing. Redundant sensors may also be used to detect errors (e.g., when there are differing measurements). These safety-critical applications include, for example, motor-controlled controls of braking or steering processes, but also the engagement of gears in gear shifts or other actuators. Wherever a high degree of reliability needs to be ensured, redundant detections are employed. This means that any error that may occur cannot lead to a failure of the entire system.In conventional motors, for example, position sensors are used for this purpose, which have a plurality of sensor elements. For example, position sensors are known which are based on the magneto-resistive effect and in which at least two chips are integrated in the position sensor (so-called "dual-die"). There, each chip can independently detect the position of the exemplary movable element. Such multichip applications, however, are generally very complicated and expensive. Moreover, it is ever the case that both chips are equally affected by errors because of their spatial and functional proximity. Thus, a short circuit can affect the two chips simultaneously. Likewise, an external disturbance can have a negative influence on all chips that use the same measurement principle.Therefore, there is a need for alternatives to replace these multichip position sensors with simple position sensors without jeopardizing the safety of the overall system.At least a part of these problems is solved by a position sensor according to claim 1 and a method for detecting a position according to claim 7. The dependent claims relate to further advantageous embodiments of the subject matter of the independent claims.The present invention relates to a position sensor for redundantly determining a position of an element which is movable by a drive motor. The position sensor includes a primary sensor and a secondary sensor. The primary sensor is configured to directly sense the position of the movable element. The secondary sensor is designed to derive the position of the movable element from at least one secondary measurement. The secondary measurement is based on a drive variable of the drive motor or on a variable caused by the movement of the drive motor.The direct position detection of the primary sensor is to be understood such that the primary sensor directly detects the position of the movable element, for example by a magnetic or optical sensor, regardless of the way in which the position of the movable element changes. In comparison, the secondary sensor is a position sensor that does not directly sense the position of the movable element, but instead senses a physical quantity defining the state of the drive motor (e.g., a movable element of the drive motor) to enable an estimate for the change in position of the movable element based thereon. For example, a drive signal for an electric motor can be used for this purpose, from which it can be derived how the position of the movable element has changed by the drive signal.The secondary sensor thus senses the cause or sequence of the movement, while the primary sensor measures or detects the resulting movement. In this way, a plurality of different signal paths are used or different approaches are used for determining the motor position for each redundant path. The paths could be different types of encoder sensors, different sensorless control algorithms, or use a combination of both approaches.Optionally, the primary sensor is a position sensor comprising at least one of the following sensor elements: a magneto-resistive element, a Hall sensor, an optical sensor, a resistance sensor.Optionally, the secondary sensor determines (or estimates) the position of the movable element based on at least one of the following variables:a voltage signal for the drive motor,a current signal for the drive motor,an electromagnetic field caused by the drive motor,a change of a magnetic field caused by the driving motor,a time duration of the drive for the drive motor,a combination thereof.Optionally, the position sensor comprises a magnetic element which is attachable to the movable element. The primary sensor can measure a change in the magnetic field caused by the movement of the magnetic element and determine the position therefrom.Exemplary embodiments also relate to a drive device having a drive motor and a movable element which is movable by the drive motor. The drive device comprises a position sensor as described above.Optionally, the drive motor can be redundantly controlled via a first phase signal and a second phase signal, wherein the first phase signal is based on sensor data of the primary sensor, and the second phase signal is based on sensor data of the secondary sensor. The first and second phase signals may be so-called phase sets, each of which is configured to drive the motor.The drive motor can be, for example, an electric motor or a three-phase motor. However, it can also comprise a linear motor or other drive elements which are designed to move the movable element. The movement of the movable element can be, for example, a rotational, linear or axial movement, such as, for example, steering movements or braking processes, but also comprise movements of a shift fork in a transmission which engages in shift elements in order to shift gears of a transmission. When the movable member performs rotational movements, the detected position is an angular position of the movable member. It is likewise possible for a combination of axial movements and rotational movements to be detected by the primary sensor and / or the secondary sensor, in order to still ensure reliable position determination in the event of failure of one of the two sensor elements.Exemplary embodiments also relate to a method for redundantly ascertaining a position of an element which is movable by a drive motor. The method comprises:directly detecting the position of the movable element by means of a primary sensor; andderiving the position of the movable member by a secondary sensor based on a driving amount of the driving motor.Optionally, the method further comprises calibrating the secondary sensor using measurement data acquired by the primary sensor.It is understood that the primary sensor may also be calibrated. For this purpose, the position can be determined by means of another measuring method. For calibration of the secondary sensor, the drive motor can execute a movement of the movable element, wherein the movement of the movable element is detected by the primary sensor and simultaneously by the secondary sensor. The resulting calibration data can be correspondingly stored in an evaluation device which can then perform a redundant detection of the position of the movable element based on sensor data from both sensor elements.It is understood that all the functions of the position sensor described above are carried out as further optional method steps according to further exemplary embodiments. In addition, it should be understood that the order of naming is not necessarily an order in executing the method steps. The steps may also be performed in a different order. Only a part of the method steps need be carried out.The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the various embodiments, which, however, should not be taken to limit the disclosure to the specific embodiments, but are for explanation and understanding only. FIG. 1 shows a position sensor according to an embodiment of the present invention. FIG. 2 shows a schematic flow diagram for a method for redundantly ascertaining a position of a movable element according to an exemplary embodiment.FIG. 1 shows an exemplary embodiment of the position sensor. The position sensor detects a position of an element 10 which is movable by a drive motor 20. The movement can comprise an axial movement A and / or a rotational movement R. The position sensor comprises a primary sensor 110 and a secondary sensor 120 for determining the position of the movable element 10.The primary sensor 110 directly detects the movement of the movable element 10. In other words, the reason for the movement has no influence on the position measurement itself, for example whether the element 10 is moved by the drive motor 20 or is moved by another device, for example.In contrast, the secondary sensor 120 does not directly sense the movement of the element 10, but rather, for example, a physical variable which drives the drive motor 20 or which causes the driven drive motor 20. This physical variable can be, for example, a current or a voltage signal with which the drive motor 20 is driven. For example, zero crossings of the voltage or current may indicate a rotational position of the electric drive motor 20 when driven by an AC signal. From this, the rotational position of the element 10 can then be estimated or determined. The physical variable can likewise comprise a time duration. The time duration can be the length of actuation of the drive motor 20, from which a distance travelled by the movable element 10 during actuation of the drive motor 20 can in turn be determined. The secondary sensor 120 may also use an indicated voltage or an induced current signal for measurement caused by the movement of the drive motor 20 (e.g., by coils present), wherein the indicated voltage or current signal is not necessarily directly the drive signal of the motor 20, but represents a secondary signal generated by the rotor, for example.FIG. 2 shows a schematic flow diagram for a method for redundantly ascertaining a position of a movable element (as in FIG. 1 ) according to one exemplary embodiment. The method comprises at least the steps of:directly detecting the position of the movable element 10 by means of a primary sensor 110; andderiving the position of the movable member 10 by a secondary sensor 120 based on a driving amount of the driving motor 20.Optionally, the method includes calibrating the secondary sensor 120 using measurement data acquired by the primary sensor 110. This can ensure that, when the primary sensor 110 and the secondary sensor 120 function correctly, sensor data are provided which indicate the same position. If deviations occur, this can indicate a malfunction of a sensor.It goes without saying that all the above-described functions of the evaluation circuit can be designed as further optional method steps. In addition, it should be understood that the order of naming is not necessarily an order in executing the method steps. The steps can also be carried out in a different sequence or only a part of the method steps is carried out.The method may also be computer implemented, i.e. it may be implemented by instructions stored on a storage medium and capable of executing the steps of the method when run on a processor. The instructions typically include one or more instructions that may be stored in different ways on different media in or peripheral to a controller (with a processor) that, when read and executed by the controller, cause the controller to perform functions, functionalities, and operations necessary to perform a method according to the present invention.Advantages of embodiments include, among other things, that very expensive dual sensor elements can be avoided to detect the movement of the movable element 10. Such dual-die encoder sensors can therefore be replaced by more cost-effective single-die variants, which are then used as primary sensors 110. The desired redundancy is ensured via the secondary sensor 120.Thus, embodiments may be used in safety critical applications for which redundant determination of motor positions is of decisive importance in order to enable a fail operational mode. Since exemplary embodiments use a plurality of signal paths, a disturbed signal path (e.g. because of a short circuit) cannot lead to a total failure. A fault may therefore not result in a non-operational state - unlike conventional dual die motor position sensors or the conventional use of multiple position sensors where failure may render multiple sensors unusable. Thus, there is a great advantage in that the different ways of determining motor positions significantly reduce the possibility of common errors. This significantly increases the safety of the product.Furthermore, exemplary embodiments provide the advantage of flexibly retrofitting or updating sensorless algorithms over time, even if a control device is already installed in a vehicle. This allows better algorithms to be implemented and thus the engine performance to be increased over time.Overall, embodiments thus reduce costs and increase flexibility without jeopardizing safety.Conventional motors for a level 4 steering system are designed, for example, as a 2 by 3 phase set (phase signals) (e.g., set 1: XYZ and set 2: ABC), wherein each phase system is controlled via a redundant path and the motor position is determined by a dual-die encoder sensor (position sensor). According to exemplary embodiments, the dual-die encoder sensor could be replaced by a single-die sensor for one of the redundant paths. The currents required for the phase set XYZ are then calculated based on the position indicated by the magnetic field of the encoder magnet on the motor shaft (as part of the primary sensor 110). This magnetic field is detected by the encoder sensor. For the other path (phase set ABC), a sensorless motor control algorithm could be used as the secondary sensor 120. Depending on the type of algorithm, the position of the rotor may be estimated based on the characteristic of the motor 20, for example. This estimated position is then used to determine the required currents in the second phase set.The features of the invention disclosed in the description, the claims and the figures can be essential for the realization of the invention both individually and in any combination.LIST OF REFERENCE CHARACTERS10 Movable element 20 Drive motor (e.g. an electric motor) 25 Secondary measurement 110 Primary sensor 120 Secondary sensor A, R Movements (axial or rotation)

Claims

A position sensor for redundantly determining a position of an element (10), which is movable by a drive motor (20), characterized by - a primary sensor (110), which is designed to sense directly the position of the movable element (10); and - a secondary sensor (120), which is designed to derive the position of the movable element (10) from at least one secondary measurement (25), wherein the secondary measurement (25) is based on a drive variable of the drive motor (20).Position sensor according to claim 1, characterized in that the primary sensor (110) is a position sensor comprising at least one of the following sensor elements: a magneto-resistive element, a Hall sensor, an optical sensor, a resistance sensor.Position sensor according to Claim 1 or Claim 2, characterized in that the secondary sensor (120) estimates the position of the movable element (10) on the basis of at least one of the following variables: - a voltage signal for the drive motor (20), - a current signal for the drive motor (20), - an electromagnetic field caused by the drive motor (20), - a change in a magnetic field caused by the drive motor (20), - a duration of the drive for the drive motor (20).Position sensor according to one of the preceding claims, characterized bya magnetic element which can be attached to the movable element (10), wherein the primary sensor (110) measures a change in the magnetic field caused by the movement of the magnetic element.A drive device having a drive motor (20) and a movable element (10) which is movable by the drive motor (20), characterized bya position sensor according to one of the preceding claims.Drive device according to Claim 5, wherein the drive motor (20) can be redundantly actuated via a first phase signal and a second phase signal, characterized in that the first phase signal is based on sensor data of the primary sensor (110), and the second phase signal is based on sensor data of the secondary sensor (120).Method for redundantly determining a position of an element (10) which is movable by a drive motor (20), characterized by - directly detecting (S110) the position of the movable element (10) by means of a primary sensor (110); and - deriving (S120) the position of the movable element (10) by means of a secondary sensor (120) on the basis of a drive variable of the drive motor (20).Method according to claim 7, characterised bycomputing the secondary sensor (120) by means of measurement data acquired by the primary sensor (110).

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