Measuring system and drive system

Abstract

Measuring system,- with a magnet (300),- with a sensor (100) and- with a magnetic field sensor (200),- wherein the sensor (100) has a plurality of segments (111, 112, 117, 118) made of a magnetically conductive material,- wherein each segment (111, 112, 117, 118) has a wing shape with a radially outwardly directed web edge (121, 122, 127, 128),- wherein each web edge (121, 122, 127, 128) is formed obliquely to the direction of rotation (a), and- wherein each web edge (121, 122, 127, 128) is spaced from the magnetic field sensor (200) by an air gap (210), characterized in that- the magnetic field sensor (200) is located between the magnet (300) and the encoder (100) is arranged, and an electrical circuit is electrically connected to the magnetic field sensor (200) and coils of a stator of an electrically commutated DC motor (400), and from the inclination of the web edges (121, 122, 127,128) and the evaluation of the resulting magnetic field vector, an angle of rotation (θ) in the direction of rotation (θ) within a segment (111, 112, 117, 118) is absolutely detected in order to determine an absolute rotational position of the encoder (100) based on a measurement signal from the magnetic field sensor (200) within a width of a segment (111, 112, 117, 118).

Description

The present invention relates to a measuring system and a drive system. For electronically commutated DC motors, precise rotation angle information is required for control. A measuring system for determining rotational speed is known from US 2005 / 0017709 A1, which uses a Wheatstone bridge constructed from four magnetoresistive sensor elements to measure the direction of a magnetic field generated by eddy currents within the blades of a turbocharger compressor wheel. Measuring systems for determining rotational speed and / or direction of rotation by measuring induced eddy currents are also known from DE 196 23 236 A1 and DE 196 34 692 A1. From DE 10 2008 059 401 A1 and DE 10 2013 000 430 A1 measuring systems for determining a position, in particular an angular position of a sensor, are known. The invention is based on the objective of improving a measuring system for measuring an angle of rotation as much as possible. This problem is solved by a measuring system with the features of claim 1 and by a drive system with the features of claim 8. Advantageous further developments are the subject of dependent claims and are included in the description. Therefore, a measuring system is planned. The measuring system includes a magnet, a transmitter, and a magnetic field sensor. The magnetic field sensor is positioned between the magnet and the transmitter. The transmitter has multiple segments made of a magnetically conductive material. Each segment has a wing shape with a radially outward-facing rib edge. Each edge of the web is angled relative to the direction of rotation. Each edge of the bridge is separated from the magnetic field sensor by an air gap. Investigations by the applicant have shown that, in a specific embodiment, such as the one illustrated in the figures, the wing-shaped design of the segments results in a low moment of inertia. Furthermore, improved measurement resolution can be achieved by angling the web edge of the wing-shaped segments within the segment. The invention is further based on the objective of providing a drive system that is as improved as possible. This problem is solved by a drive system with the features of independent claim 1. Advantageous further developments are the subject of dependent claims and are included in the description. Therefore, a drive system is provided. The drive system features an electrically commutated DC motor and a measuring system. The measuring system includes a magnet, a transmitter, and a magnetic field sensor. The magnetic field sensor is positioned between the magnet and the transmitter. The transmitter has multiple segments made of a magnetically conductive material. Each segment has a wing shape with a radially outward-facing rib edge. Each edge of the web is angled relative to the direction of rotation. Each edge of the bridge is separated from the magnetic field sensor by an air gap. The encoder is designed to be rotationally fixed on a shaft of the electrically commutated DC motor. Investigations by the applicant have shown that in a specific embodiment, such as that explained for example in relation to the figures, the segments enable a high measurement resolution for the precise control of the commutation. The training courses described below relate to both the measuring system and the drive system. According to a beneficial further development, the mass of the segments is distributed rotationally symmetrically. Advantageously, the sensor is designed to be unbalanced. According to a particularly advantageous embodiment, the segments are arranged on a hub. Advantageously, the segments and the hub are formed in one piece from the magnetically conductive material. Advantageously, the segments and the hub are made of gray cast iron. According to an advantageous embodiment, the radially outwardly directed edge of the web of each segment is spaced from a hub of the sensor by a length of the segment. According to an advantageous embodiment, the magnetic field sensor comprises at least one first sensor element for measuring a magnetic field component in a first spatial direction and a second sensor element for measuring a magnetic field component in a second spatial direction. Particularly preferably, the magnetic field sensor comprises one first sensor element for measuring a magnetic field component in a first spatial direction, one second sensor element for measuring a magnetic field component in a second spatial direction, and one third sensor element for measuring a magnetic field component in a third spatial direction. According to an advantageous further development, the segments are designed to generate an airflow during a rotary movement of the sensor. According to an advantageous embodiment, the drive system comprises an electrical circuit. This circuit is electrically connected to the magnetic field sensor and the coils of a stator of the electrically commutated DC motor. Advantageously, the electrical circuit is configured to determine the absolute rotational position of the encoder based on a measurement signal output by the magnetic field sensor within a segment width. According to an advantageous further development, all segments have the same shape, so that predominantly periodic measurement signals are generated from segment to segment. The previously described advanced training variants are particularly advantageous both individually and in combination. All advanced training variants can be combined with one another. Some possible combinations are explained in the description of the exemplary embodiments shown in the figures. However, the combinations of advanced training variants presented there are not exhaustive. The invention will now be explained in more detail by means of exemplary embodiments based on graphic representations. Figure 1 shows a schematic representation of a measuring system, Figure 2 a schematic representation of a drive system, Figure 3 a schematic view for different rotation angles, and Figure 4 a schematic diagram of a sensor signal. Figure 1 schematically depicts a measuring system comprising a magnet 300, a magnetic field sensor 200, and an encoder 100 made of magnetically conductive material in a three-dimensional view. It should be noted that it is also sufficient to make only the vanes of a magnetically conductive material. Also shown are a rotation axis 140 of the encoder 100 and a direction of rotation a of the encoder 100. In one embodiment of Figure 1, the magnetic field sensor 200 is configured to measure the mutually orthogonal flux density components Bx, By, and Bz in three spatial directions. In one embodiment of Fig. 1, the magnet 300 is a permanent magnet, e.g., made of SmCo217. The magnetic field sensor 200 is arranged between the magnet 300 and the encoder 100. Both the magnet 300 and the magnetic field sensor 200 are fixed in position. The encoder 100, however, is movable relative to the magnet 300 and the magnetic field sensor 200, in particular rotatable about the axis of rotation 140. The magnetic field of the magnet 300 penetrates the magnetic field sensor 200 and is modulated by the encoder 100. Such a magnet 300 is also referred to as a back-bias magnet. The encoder 100 has a plurality of segments 111, 112, 117, 118, which are formed from a magnetically conductive material. In one embodiment of Fig. 1, the encoder 100 has, for example, seven segments, with only segments 111, 112, 117, 118 being visible in Fig. 1. Each of the segments 111, 112, 117, 118 in one embodiment of Fig. 1 has a wing shape. The wing shape is formed by a flat or, preferably, a curved plate. Each of the segments 111, 112, 117, 118 has at least one predominantly radially outwardly directed web edge 121, 122, 127, 128. In the embodiment of Fig. 1, each segment 111, 112, 117, 118 also has two side edges that are predominantly axially oriented. Each segment 111, 112, 117, 118 is inclined to the direction of rotation a. The inclined web edge 121, 122, 127, 128 is therefore neither parallel to the axial direction nor parallel to the direction of rotation. Each segment 111, 112, 117, 118 is designed as a wing-like web. The inclined position of segments 111, 112, 117, 118 results in a fan-like effect during rotation. Due to the inclined web edges 121, 122, 127, 128, the resulting magnetic field vector of the magnetic field components Bx, By, and Bz, as shown in Figs. 2 and 4, allows for the absolute detection of a rotation angle φ in the direction of rotation a within a segment 111, 112, 117, 118. An output signal S of the magnetic field sensor 200 is a function of the rotation angle φ. The rotation angle from segment 111 to segment 112 can be determined by incrementing (counting). The web edge 121, 122, 127, 128 of each segment 111, 112, 117, 118 is – as schematically shown in Fig. 2 – spaced from the magnetic field sensor 200 by an air gap 210. The air gap 210 is, for example, 2 mm for each segment 111, 112, 117, 118. For a constant air gap 210, all sections of the web edge 121, 122, 127, 128 can be formed at the same distance from the axis of rotation 140. The segments 111, 112, 117, 118 are mechanically connected to a hub 110 for mounting on a shaft. In one embodiment of Fig. 1, the segments 111, 112, 117, 118 and the hub 110 are formed in one piece from a magnetically conductive material. For example, the encoder 100 is manufactured using a gray cast iron process. Several advantages are achieved with a measuring system according to an embodiment of Fig. 1. The measuring system offers robust acquisition of the absolute rotational position of the encoder 100, even for industrial and automotive applications in the presence of dirt, oil mist, etc. Magnet 300 and magnetic field sensor 200 are located far from the center of rotation and are orthogonal to the axis of rotation 140. Due to the relatively large radius, resulting from the large length L of segments 111, 112, 117, 118, a higher resolution is achieved compared to measuring systems located close to the center of rotation. Despite the large radius, the wing shape of segments 111, 112, 117, 118 ensures a sufficiently low moment of inertia. Vibrations and measurement tolerances are reduced because no gearbox is required for data acquisition. Furthermore, depending on the direction of rotation a, segments 111, 112, 117, 118 can synergistically cool elements by convection. The embodiment shown in Fig. 1 can, in principle, be used for various rotary movements to be detected. Due to the circumferential division of segments 111, 112, 117, 118, the measuring system is particularly optimized for measuring the rotations of electric motors. A drive system with a measuring system according to Fig. 1 is shown in the schematic sectional view of Fig. 2. Fig. 2 shows an electrically commutated motor 400, for example a stepper motor or an electrically commutated DC motor, also known as a BLDC motor. The motor 400 in the embodiment of Fig. 1 has a rotor 430 on a motor shaft 410. The rotor 430 rotates within the stator 420. The rotor 430 has, for example, permanent magnets. The stator 420 has coils. The coils of the stator 420 are connected to a circuit 500. The circuit 500 is configured to control a coil current through the coils of the stator 420. To control the coil current by the circuit 500, the measurement of the rotational position by means of the measuring system is required. According to one embodiment of Fig. 2, the electrical commutation is particularly precise because the absolute rotational position is detected, and the switching point for commutation can be determined in time with the change in the absolute rotational position. In the embodiment of Fig.The segments (not shown) of the encoder are fixedly assigned to 100 motor pole pairs (not shown). The position of the segments on the circumference of the encoder is mechanically adjusted to the pole pairs of the motor 400 to enable precise detection of the rotor position 430 by means of the measuring signal S by the circuit 500. Fig. 3 shows a magnetic field sensor for two (2D) or three (3D) magnetic field components. The magnetic field sensor 200 is biased by a backbias magnet. The backbias magnet is not shown in Fig. 3 for clarity. Fig. 3 shows the edge 121 of segment 111 in different successive rotational positions φ1, φ2, φ3, φ4, φ5 relative to the magnetic field sensor 200. The position of the edge of segment 111 changes continuously during a movement of the segment past the magnetic field sensor 200. Any non-linear properties of the magnetic field sensor 200 or fluctuations in field intensity versus angle can be at least partially compensated mechanically by the geometry of segments 111, 112, 117, 118. A maximum signal amplitude is utilized within segments 111, 112, 117, 118. This results in a higher signal-to-noise ratio (S / N) compared to a system with a signal amplitude exceeding 360°. Consequently, a high overall resolution for the measurement system is achieved because the signal amplitude for each segment 111, 112, 117, 118 is available individually for position resolution within the segment. Accordingly, the commutation of motor 400 of an embodiment from Fig. 4 can take place at a precise time. The jump at angle φ5 marks a change in the commutation. This jump simultaneously and automatically generates a synchronization pulse, which belongs to the next winding in the stator 420. Fig. 4 schematically shows a diagram of a measurement signal S with the magnetic flux density components Bx, By, and Bz in three spatial directions as a function of the rotation angle φ. The rotation angle positions φ0 and φ5 mark a transition from one segment to the next. The circuit is configured to calculate the time for the next winding of the stator 420 in the commutation by analyzing the values ​​of the magnetic flux density components Bx, By, and Bz. The next winding is, in effect, announced by this behavior. The invention is not limited to the embodiments shown in Figures 1, 2, 3 to 4. For example, it is possible to provide a different wing-like shape for the segments. It is also possible to provide a larger or smaller number of segments, particularly adapted to the poles of the electric motor. The functionality of the drive system according to Figure 2 can be used particularly advantageously for high-speed or electro-hydraulic applications. For example, the drive system is used in motor vehicles for an ABS system, a brake booster, or a power steering system. Reference symbol list 100 Encoder 111, 112, 117, 118 Segment 121, 122, 127, 128 Web edge, edge 140 Rotation axis 200 Magnetic field sensor, Hall sensor 210 Air gap 300 Magnet, permanent magnet 400 Electric motor 410 Shaft 420 Stator 430 Rotor 500 Circuit S Signal a Direction of rotation φ, φ0, φ1, φ2, φ3, φ4, φ5 Angle of rotation Bx, By, Bz Magnetic field component, flux density component B Flux density

Claims

Measuring system,- with a magnet (300),- with a transmitter (100) and- with a magnetic field sensor (200),- wherein the transmitter (100) has a plurality of segments (111, 112, 117, 118) made of a magnetically conductive material,- wherein each segment (111, 112, 117, 118) has a wing shape with a radially outwardly directed web edge (121, 122, 127, 128),- wherein each web edge (121, 122, 127, 128) is formed obliquely to the direction of rotation (a), and- wherein each web edge (121, 122, 127, 128) is spaced from the magnetic field sensor (200) by an air gap (210), characterized in that- the magnetic field sensor (200) is located between the magnet (300) and the encoder (100) is arranged, and an electrical circuit is electrically connected to the magnetic field sensor (200) and coils of a stator of an electrically commutated DC motor (400), and from the inclination of the web edges (121, 122, 127,128) and the evaluation of the resulting magnetic field vector, an angle of rotation (φ) in the direction of rotation (α) within a segment (111, 112, 117, 118) is absolutely detected in order to determine an absolute rotational position of the encoder (100) based on a measurement signal from the magnetic field sensor (200) within a width of a segment (111, 112, 117, 118). Measuring system according to claim 1, characterized in that the mass of the segments (111, 112, 117, 118) is rotationally symmetrically distributed. Measuring system according to one of the preceding claims, characterized in that the segments (111, 112, 117, 118) are arranged on a hub (110). Measuring system according to claim 3, characterized in that the segments (111, 112, 117, 118) and the hub (110) are formed in one piece. Measuring system according to one of claims 3 or 4, characterized in that the segments (111, 112, 117, 118) and the hub (110) are made of grey cast iron. Measuring system according to one of the preceding claims, characterized in that the magnetic field sensor (200) has at least a first sensor element for measuring a magnetic field component (Bx) in a first spatial direction and a second sensor element for measuring a magnetic field component (By) in a second spatial direction and / or a third sensor element for measuring a magnetic field component (Bz) in a third spatial direction. Measuring system according to one of the preceding claims, characterized in that the segments (111, 112, 117, 118) are designed to generate an airflow during a rotary movement of the sensor (100). drive system- with a measuring system according to one of the preceding claims,- wherein the encoder (100) is designed to be rotationally fixed on a shaft (410) of the electrically commutated DC motor (400). Drive system according to claim 8, comprising an electrical circuit (500) which is electrically connected to the magnetic field sensor (200) and coils of a stator (420) of the electrically commutated DC motor (400), characterized in that the electrical circuit (500) is configured to determine an absolute rotational position of the encoder (100) based on a measurement signal (S) output by the magnetic field sensor (200) within a width of a segment (111, 112, 117, 118).

Images