WO2000017661A1

WO2000017661A1 - Device and method for detecting the movement of rotation of a shaft

Info

Publication number: WO2000017661A1
Application number: PCT/DE1999/002772
Authority: WO
Inventors: Hubert Lamm; Günter HADERER
Original assignee: Robert Bosch Gmbh
Priority date: 1998-09-21
Filing date: 1999-09-02
Publication date: 2000-03-30
Also published as: DE19842990A1

Abstract

The invention relates to a device for detecting the movement of rotation of a shaft (3), comprising a flux modulator (5, 15) that rotates with the shaft and through which a magnetic circuit runs, whereby the flux modulator (5, 15) modulates the flux in the magnetic circuit with n number of periods per rotation of said shaft (3). The device also comprises a magnetic field sensor (7) for detecting fluctuations in the magnetic field in the magnetic circuit that are caused by the rotation of the flux modulator (5, 15), in addition to a comparator (23, 24) that compares the output signal of the magnetic field sensor (7) with a threshold value. The comparator (23, 24) emits a signal that indicates a movement of rotation when the output signal of the magnetic field sensor (7) exceeds the threshold value in a given direction. No signal is emitted when the output signal exceeds the threshold value in the opposite direction. The movement of rotation can thus be detected with a certain amount of tolerance with respect to inaccuracies and drifting of said threshold value.

Description

Device and method for detecting the rotational movement of a shaft

The invention relates to a device for detecting the rotary movement of a shaft with the features mentioned in the preamble of claim 1 and a method for detecting such a rotary movement.

State of the art

Devices and methods of the type mentioned are used in many technical areas in order to detect and quantitatively measure rotary movements, for example of electric motors. A special field of application for such devices and methods are control systems for the drive motors of sunroofs or window regulators, which automatically switch off the drive motors when the sunroof or the window pane has reached an end of its / its range of motion.

In such systems it is possible to use automatic switch-off devices which interrupt the power supply of a drive motor if it is detected that it no longer rotates because the Window or the sunroof has reached a stop at the end of the range of motion.

A disadvantage of such systems, however, is that with each actuation, the transmission downstream of the engine experiences a violent vibration when the sunroof or window reaches its stop and is thereby unnecessarily stressed.

It is therefore desirable to always be able to track the position of such a window or sunroof precisely in order to be able to stop the motor or limit its driving force in good time before the stop at the end of the movement range.

For this purpose, different devices for detecting the rotary movement of a drive shaft have been developed. A known solution uses a circular disk-shaped magnet mounted on the shaft, the north and south poles of which are separated by a plane running through the shaft. A Hall sensor is arranged in a stationary manner in a magnetic circuit which runs through this magnet. Due to its rotation, the disk-shaped magnet modulates the flux sensed by the Hall sensor with a period which corresponds to the rotation period of the shaft. The Hall sensor generates a signal which, depending on the sign of the flow, can have two different values. A wide range of tolerance influences, which are related, for example, to the magnetic flux, the arrangement of the Hall sensor or the switching hysteresis of the Hall sensor, result in one of the two output levels of the Hall sensor in most cases lasts longer than the other. It does not therefore indicate every level change a rotation of 180 degrees. In order to be able to computationally compensate for such an inaccuracy, it is necessary to observe the output signal of the Hall sensor over several periods and to form an average.

Another such device is known from DE-A-19525292. This known device for detecting a rotary movement comprises a flow modulator in the form of a circular disc with two cut segments, which, mounted on the shaft, rotates between two pole pieces of a stationary magnetic circuit. If the areas of the circular disk that have not been cut off lie opposite the pole pieces, the air gap in the magnetic circuit is considerably smaller than if the cut off areas lie opposite the pole pieces. As a result, the flux in the magnetic circuit varies with two periods per revolution of the shaft. A Hall sensor is arranged laterally next to the magnetic field source of the magnetic circuit and detects its leakage flux, which is also modulated by the rotation of the circular disk.

The Hall sensor of this known device generates two output signals "0" or "l ^w or" H "and" L ^u , depending on how large the magnetic field strength to which it is exposed. For this it is necessary to define a field strength value between the two extreme values at which the output signal switches from one level to the other. This value depends on the local conditions of the magnetic circuit in which the hall sor is used. In order to ensure that the Hall sensor switches between the two levels at an angular distance of 90 degrees, a complex adjustment is required.

Advantages of the invention

The device according to the invention for detecting a rotary movement with the features of claim 1 and the method according to claim 9 have the advantage that the accuracy of the rotary movement detection is independent of the threshold value set, so that the threshold value is any value within the fluctuation - Width of the output signal of the magnetic field sensor can be selected. The accuracy of detection of the device and the method are therefore not affected by mechanical changes in the magnetic circuit, for example as a result of aging or wear of moving parts, by thermal expansion or shrinking phenomena due to the ambient temperature, etc.

The resolution in the rotational movement detection that can be achieved with the device according to the invention or the method according to the invention depends on the number n of periods with which the flux modulator modulates the flux in the magnetic circuit per revolution of the shaft. This number n should be at least 3.

The flow modulator is preferably a wheel mounted on the shaft itself, on which, in the circumferential direction of the wheel, alternate n areas with a first one Magnetic permeability and n areas with a second magnetic permeability are arranged, which alternately move through the magnetic circuit when the shaft rotates and thus modulate its magnetic flux.

According to a preferred embodiment, the wheel is a gearwheel, and the areas with different magnetic permeabilities are the teeth or the interdental spaces of the gearwheel.

Alternatively, the wheel may be a disc with holes arranged circumferentially at a given radius.

In order to enable a high magnetic flux in the magnetic circuit, this further comprises at least one stationary pole shoe which faces the wheel and whose width is at most equal to the width of each area. A corresponding second pole piece can be arranged at another point facing the wheel, the position being chosen so that both pole pieces face either areas with high permeability or areas with low permeability at any time.

According to an advantageous further development of the invention, which not only enables the extent of a movement, but also its direction, to be detected, a second magnetic field sensor is arranged at an angle relative to the first magnetic field sensor about the axis of the shaft, the angle being chosen such that an output signal of the second magnetic field sensor a phase shift relative to Output signal of the first, which is measurably different from 0 or ± π. The direction of rotation of the shaft can be identified by comparing the chronological sequence, for example of zero crossings of the output signals of the two magnetic field sensors.

The second magnetic field sensor can be arranged to detect fluctuations in the magnetic flux in the same magnetic circuit as the first magnetic field sensor, but is preferably assigned to a separate, second magnetic circuit.

Further advantageous features of the invention can be found in the following description of exemplary embodiments.

drawings

The invention is explained in more detail below on the basis of several exemplary embodiments with reference to the associated drawings. Show it:

Figure 1 shows the basic structure of an armature shaft with an armature and an inventive device for detecting the rotational movement of the shaft;

FIG. 2 shows a first embodiment of the device according to the invention in a view in the direction of the shaft;

Figures 3 each show a further embodiment in and 4 perspective view; Figure 5 is a circuit diagram of a magnetic field sensor and a comparator according to the invention;

Figure 6 waveforms of signals in the circuits of Figures 5 and 7; and

Figure 7 is a circuit diagram of a device according to the invention, which is able to detect the direction of rotation.

Description of the embodiments

Figure 1 shows a side view of an armature 1 of an electric motor, which is mounted together with a commutator 2 on an armature shaft 3. A drive screw 4 at one end of the shaft 3 drives a window lifter mechanism or a sunroof of a motor vehicle via a gear wheel (not shown) with an axis perpendicular to the armature shaft 3.

A metal gear wheel 5 is fixedly mounted on the shaft 3 between the drive screw 4 and the armature 1. A magnet 6 is arranged in a stationary manner at a distance from the outer circumference of the gear wheel 5. The space between the magnet 6 and the gear 5 is essentially filled by a magnetic field sensor in the form of a Hall sensor 7.

A magnetic flux runs from the magnet 6 through the Hall sensor 7 into the gear wheel 5. This flux is of different strength, depending on whether the Hall sensor on the gear wheel has a tooth or a space between the teeth opposite. These fluctuations in the magnetic flux are registered by the Hall sensor and processed by electronic circuits, which will be discussed in more detail later, in particular in connection with FIGS. 5 and 6.

FIG. 2 shows the rotary motion detection device from FIG. 1 in a side view along the axis of the shaft 3. A magnetic circuit here extends from the magnet 5 via the Hall sensor 7 and an air gap in a tooth 8 of the gear wheel 5. An adjacent tooth 8 has a pole piece 10 opposite, from which the magnetic flux is returned via a yoke 11 to the magnet 6.

In the position of the gearwheel 5 shown, the air gaps between the Hall sensor 7 or the pole shoe 10 and the gearwheel 5 are narrow, and accordingly the flow through the Hall sensor is strong. If the gear wheel 5 rotates in one direction or the other, an interdental space 9 comes to lie opposite the Hall sensor 7 or the pole piece 10, and the flow through the Hall sensor 7 accordingly decreases. The Hall voltage proportional to the magnetic field strength in the Hall sensor is tapped and processed, as will be explained later.

The width of the pole piece 10 or the Hall sensor 7, which in this embodiment also has the function of a pole piece, namely to guide the flow into the gearwheel with as little scatter as possible, is not greater in circumferential direction than the width of the teeth 8 or the interdental spaces 9 of the gear 5; preferably ^"it is slightly smaller in order to achieve the greatest possible modulation of the magnetic flux by the rotation of the gear wheel 5.

The function of the yoke 11 can also be taken over by a metallic housing of the detection device.

A second arrangement of magnet 6 ', Hall sensor 7', pole piece 10 'and yoke 11' is arranged on the gear wheel 5 offset at an angle about the axis of the shaft 3. The angle is chosen so that whenever the Hall sensor and pole piece of one arrangement are exactly opposite a tooth or a tooth space, the Hall sensor and pole piece of the other arrangement are half a tooth and half a tooth space. Because of this arrangement, output signals are obtained from the two Hall sensors 7 and 7 ', which are out of phase with each other by ± π / 2. The evaluation of these signals will be discussed later in connection with FIGS. 7 and 8.

Figure 3 shows an alternative embodiment of a detection device according to the invention. In this embodiment, the magnet 6 is oriented parallel to the shaft 3 and arranged so that there is only a small air gap between it and an opposite tooth 8 of the gear wheel 5. In this position shown in the figure, the magnetic flux from the magnet 6 largely runs through the tooth 8, and the stray field, which is detected by the Hall sensor 7 arranged on the side of the magnet 6 facing away from the gear, is small. If the tooth wheel 5 rotates further, so that the magnet has a tooth space 9 opposite, its magnetic field is distributed more evenly over the space surrounding the magnet 6, and the field detected by the Hall sensor 7 has a stronger effect. The signal detected by the Hall sensor of this embodiment thus behaves, so to speak, in phase opposition to the signal recorded in the previous embodiment, but is evaluated in the same way.

Of course, a second magnet and a second Hall sensor can also be provided in this embodiment, which detects a phase-shifted signal.

FIG. 4 shows a third embodiment, in which the gearwheel is replaced by a circular metallic disk 15, into which, at a given radius n, axially extending holes 19 are broken, which form regions of low permeability. The diameter of the holes are essentially equal to the width of the areas between two adjacent holes, which have a higher permeability.

The disk 15 rotates between the two arms of a horseshoe-shaped magnet 6. These arms carry pole shoes 10 on their inner ends facing the disk 15, the cross sections of which essentially correspond to that of the holes 19 and only one of which can be seen in the figure . A Hall sensor (not shown) is arranged on one of the pole shoes. Just as with the devices described above, the Hall sensor produces a periodic signal which has n periods per revolutions of the shaft 3.

FIG. 5 schematically shows the electronic components which are used in the device according to the invention for detecting the rotary movement. The Hall sensor 7 has a first connection pair for a supply current and a second connection pair 21, 22 for tapping a Hall voltage induced by the magnetic field. The terminal 21 is kept at an intermediate potential between a supply potential Vcc and ground by a voltage divider R1, R2. The other terminal 22 is connected to a first input of an operational amplifier 23, the second input of which is supplied with a potential via a voltage divider R3, R4, which potential is selected such that it lies between the extreme values of the potential at the terminal 22. The operational amplifier 23 outputs the square-wave signal shown in FIG. 6, line a with n periods per armature revolution. The ratio of the periods of high and low levels within a period of the output signal of the operational amplifier 23 depends on the value of the potentials set by the voltage dividers R1, R2 or R3, R4. However, these relative time periods are not evaluated. Instead, the output signal of the operational amplifier 23 is fed to a flip-flop 24, which in each case generates a short pulse on a rising edge of the output signal, but ignores the falling edges. The operational amplifier 23 thus forms, together with the flip-flop 24, a comparator which supplies a pulse when the signal from the Hall sensor is via a value defined by the voltage divider R3, R4 increases, but not when it falls below this value again. This gives the pulse signal shown in FIG. 6, line b, with n pulses per revolution of the shaft. The number of pulses output by the multivibrator 24 can be recorded by a counter 25 in order to obtain a measure of the angle of rotation of the shaft 3.

Figure 7 shows the electronic components of the device according to the invention in the event that a second magnetic field sensor 7 'is provided, as shown in Figure 2. The evaluation circuit, which is formed by the components lying within the dashed box 20 in FIG. 5, is shown in simplified form in FIG. 7 by a box 20. The output signal of the evaluation circuit 20 is present at the counter input C of a counter 25. As in FIG. 5, an output connection of the Hall sensor 7 'is connected to the center point of a voltage divider R1', R2 '. The other output terminal 22 'is connected to an input of an operational amplifier 23', the second input of which is connected to a second voltage divider R3 ', R4'. The potentials set by the two voltage dividers are again chosen such that the potential difference at the inputs of the operational amplifier 32 'changes its sign when the field sensor 7' changes from high to low. Due to the relative arrangement of the Hall sensors 7 and 7 ', as described with reference to FIG. 2, the output signal of the operational amplifier 23' (see FIG. 6, line c) is against the output signal of the sensor 7 shown in line a by π / 2 out of phase. This output signal of the Hall sensor 23 'is applied to a counter direction input U / D of the counter 25, so that, depending on the level at this input, a pulse arriving at the input C leads to an increase or decrease in the counter reading of the counter 25 by 1.

It is obvious that the circuit shown in FIG. 7 delivers correct results even if the phase shift of π / 2 does not deviate by more than π / 4. In principle, it is sufficient to distinguish the directions of rotation if the phase shift between the output signals of the operational amplifiers 23 and 23 'deviates so far from 0 or ± π that the difference can be recognized by a downstream evaluation circuit.

This gives a device for detecting the rotational movement of a shaft, which makes it possible to achieve a high angular resolution with little effort, which is essentially only possible by the possible number n of areas of different permeability, ie. H. in the examples described here, the number of holes or interdental spaces or teeth is limited which can be accommodated on a wheel in such a way that the flow change caused by them can be reliably detected.

In order to reduce the sensitivity of the device to contamination, the interdental spaces or holes can be filled with a solid material whose magnetic permeability differs significantly from that of the gear wheel or the disk. In such a case it is also mδcj- Lich, a gear or a disc made of a material with low permeability, such as a plastic, and to fill the holes or interdental spaces with a metal of high permeability.

Claims

claims

1. Device for detecting the rotary movement of a shaft (3) with a flow modulator (5,15) rotating with the shaft, through which a magnetic circuit runs, the flow modulator (5,15) the flow in the magnetic circuit with a number n of periods modulated per revolution of the shaft (3), a magnetic field sensor (7) for detecting fluctuations in the magnetic flux caused by the rotation of the flux modulator (5, 15) in the magnetic circuit and a comparator (23, 24) for comparing the output signal of the magnetic field sensor (7 ) with a threshold value, characterized in that the comparator (23, 24) outputs a signal indicating a rotational movement when the output signal of the magnetic field sensor (7) exceeds the threshold value in a given direction and does not output a signal when the output signal exceeds the threshold value in the opposite direction.

2. Devices according to claim 1, characterized in that n is at least equal to three.

3. Device according to claim 2, characterized in that the flow modulator comprises a wheel (5, 15) mounted on the shaft (3), on which in the circumferential direction alternatingly n regions (8) with a first magnetic permeability and n regions ( 9,19) are arranged with a second magnetic permeability.

4. The device according to claim 3, characterized in that the wheel is a gear (5) and the areas of the teeth (8) and the interdental spaces

(9) of the gear.

5. The device according to claim 3, characterized in that the wheel is a disc (15) with holes arranged in the circumferential direction (19).

6. Device according to one of claims 3 to 5, characterized in that the magnetic circuit comprises at least one pole piece (10) which faces the wheel (5,15) and whose width is at most equal to the width of each area (8,9,19 ) is.

7. Device according to one of the preceding claims, characterized in that a second magnetic field sensor (7 ') relative to the first magnetic field sensor (7) around the axis of the shaft (3) is arranged at an angle, the angle being selected so that an output signal of the second magnetic field sensor (7 ') has a phase shift relative to the output signal of the first (7) which is measurably different from 0 or + π.

8. The device according to claim 7, characterized in that the second magnetic field sensor (7 ') detects fluctuations in the magnetic flux in a second magnetic circuit.

9. A method for detecting the rotary movement of a shaft with the aid of a magnetic circuit which runs through a flux modulator (5; 15) which rotates with the shaft (3) and modulates the flux in the magnetic circuit with n periods per revolution of the shaft (3), with the steps: a) measuring a first magnetic flux at a predetermined point (7) of the magnetic circuit, b) comparing the measured first magnetic flux with a threshold value, c) generating a signal indicating a rotational movement if the measured first magnetic flux has the threshold value in a given Direction exceeds, but not if the measured first magnetic flux exceeds the threshold value in the opposite direction.

10. The method according to claim 9, with the additional steps: d) measuring a second magnetic flux at a second location (7 ') of a magnetic circuit, e) comparing the measured second magnetic flux with a second threshold value, f) detecting whether at the time which one of the magnetic fluxes exceeds the assigned threshold value in a specific direction, the other magnetic flux lies above or below the threshold value assigned to it, and recognizing the direction of rotation based on the result of the detection.