WO2003044468A1

WO2003044468A1 - Rotating switch unit with additional switching function

Info

Publication number: WO2003044468A1
Application number: PCT/EP2002/013001
Authority: WO
Inventors: Axel Bartos; Dirk Schmitz; Armin Meisenberg
Original assignee: Hl-Planar Technik Gmbh
Priority date: 2001-11-23
Filing date: 2002-11-20
Publication date: 2003-05-30
Also published as: AU2002356695A1; DE10157565A1; DE10157565B4

Abstract

The invention relates to a contact-free sender with a signal transmitting unit and a signal receiver unit, whereby the digitised output voltages of the signal receiver unit are analysed as, for example, counter or rotation-direction signals. Further positional information can be obtained from the dependence of the output signal amplitudes, applied in one embodiment as a function of the separation of the signal transmission unit from the signal receiver unit, which can be used as a further digital signal to extend the switching range.

Description

"Rotary switch unit with additional switching function"

The invention relates to an encoder, in particular a rotary switch unit, the switching stages are run through by turning a rotary knob.

For the contactless detection of the rotary movement of an axis, rotation angle sensor units are known in which a ferromagnetic (passive) or permanent magnetic (active) pole wheel is fixedly connected to the axis, which emits signals when it rotates with the axis, which signals are then detected by a measurement sensor. When the magnet wheel rotates, the resulting signals can be measured in the form of magnetic field changes with the help of active sensors in the form of a Hall element or a magnetoresistive bridge. The sensors respond in an effect-specific manner to modulations of the flux density or the field strength of the signal transmitter and output electrical signals after a magnetoelectric conversion of the field strength changes.

As can be seen, for example, from US Pat. No. 4,628,259, by evaluating counting pulses of an n-pole magnet wheel, the rotational position of the magnet wheel, ie the angular position in the direction of rotation of the axis, can also be determined. In the simplest case, this can be done either by a The output signals are digitized correctly using a threshold switch or by digitally querying the current signal level after analog-to-digital conversion with more than 1 bit resolution and subsequent control of a digital counter with counting and counting direction input.

As a result, you can use this type of non-contact sensors to determine the angle of rotation position, the speed, the speed of rotation, the acceleration and the direction of rotation of the axis.

The object of the invention is to provide an inexpensive rotary switch unit which allows additional switching functions.

According to the invention the object is achieved by the object characterized in claim 1.

Advantageous developments of the invention emerge from the respective subclaims.

Magnetic field sensors in the sense of this invention are to be understood in particular to mean all magnetoresistive sensors which make use of one of the XMR technologies. Various XMR technologies (AMR, GMR, CMR, GMI) are described in "Stefan Mengel, Technology Analysis Magnetism, Volume 2: XMR Technologies, VDI Technology Center Physical Technologies", to which content is referred.

According to the invention, a transmitter is provided, which by the arrangement of a signal pickup unit relative to a signal transmitter unit, a contactless measurement z. B. the rotational angle position of the rotary switch enables, the switching stages can be determined by the number of recorded signals. According to the invention, the basic idea can be achieved by a rotary switching function with a plurality of switching stages with one consisting of a pole wheel with n Realize magnetic poles as a pulse generator unit and a magnetoresistive sensor as a pulse pick-up unit existing rotary sensor. Hall sensors can also be used instead of magnetic field sensors.

When the magnet wheel rotates past the sensor with n-ferro- or permanent-magnetic poles, a magnetoresistive sensor detects, for example, the changes in field strength by the passage of a respective pole, so that in this case there are n switching steps per revolution of the magnet wheel. The rotary switch can be turned endlessly without specifying a zero position.

According to an advantageous embodiment of the invention, the switching function of the rotary switch is expanded by the detection of the signal emitted from the respective pole of the magnet wheel to the magnetoresistive sensor and by the detection of the magnetic field strength. The signal strength of the signal is advantageously set as a function of the distance between the magnet wheel and the sensor unit, so that a change in this amplitude results in a change in amplitude.

In the following, the physical-technical structure is explained in more detail, which can be divided into two switching functions, i.e. can be divided into the rotary switching range and the linear switching range dependent on the signal amplitude.

The magnetoresistive sensor advantageously has two outputs, at each of which a first and a second output signal is output. The first output signal essentially corresponds to a signal which is sinusoidal in the first approximation, while the second output signal is an essentially cosine-shaped signal in the first approximation. These two output signals are read out in a phase-shifted manner and digitized in an analog-digital converter, so that ultimately a counting or direction of rotation signal is present. A suitable phase shift is for example Vi period of the output signals. With the aid of this signaling, a change in the rotational position for the rotary switching range can be determined by comparing the amplitudes with one another.

According to an advantageous development of the invention, a threshold switching unit is provided for the rotary switching range, with which the two output signals are each converted into binary sensor signals with constant amplitude, the rotational position of the magnet wheel being determined from the flank change of the amplitudes. A conventional amplifier / trigger circuit, for example, which triggers when a certain value is exceeded can serve as the threshold value switching unit. Such a circuit can consist of two triggers with a switching threshold at 0 mV / V, which generate a counting pulse and a direction of rotation signal for the digital counter from the two magnetoresistive bridge signals.

According to the invention, a further signal is now advantageously obtained for the linear switching range from the course of the characteristic curve of the output signals, in order to be able to obtain further, additional location information beyond the angular position of the pole wheel. This further information is set as a function of the distance, which can be varied by a relative movement of the magnet wheel away from the sensor or towards it in a direction of movement that is essentially perpendicular to the plane of rotation.

Thus, in an embodiment for the rotary switching function, an additional switching function can be implemented, by means of which a relative linear movement between the magnet wheel and the sensor in the above direction of movement distinguishes the "magnetic field strong" state from the "magnetic field weak" state. When the two output signal voltages are evaluated simultaneously, these two states "magnetic field strong" and "magnetic field weak" can then be recognized in any rotational angle position. In order to reliably maintain the rotary switching function even in the "weak magnetic field" state and to eliminate the generation of incorrect rotary signals, the characteristic curves are analyzed in a certain threshold value range in an advantageous development of the invention. This range corresponds to the upper limit of the amplitude, that is to say the maximum output voltage value of the analog output signal, the lower limit being limited by the voltage value of the analog output signal above which a measurement of the angular position of the magnet wheel is still possible reliably.

For each output signal of the sensor, the threshold value range is determined by two threshold values, the switching thresholds of the lower limit advantageously being selected such that in the "magnetic field strong" state, at least one of the two output signals is always outside the threshold value range. In this embodiment, it can be determined by means of the threshold switches whether the amount of the output voltage of one of the two sensor outputs exceeds a defined limit or whether the amount of both output voltages of the respective sensor outputs is simultaneously below the defined limit.

Because of this switching device, the switching function of the contactless rotary switch is expanded with the aid of the switching function realized by a linear displacement of the magnet wheel relative to the sensor.

According to an advantageous embodiment, the circuit function is intended to interrupt the forwarding of the counting and counting direction signal of the rotation detection when the "magnetic field weak" state is determined.

Corresponding to an edge comparison of the amplitudes converted into binary signals to determine the rotational position, the threshold value exceeding signals of the linear circuit area also become in a manner corresponding to the rotary switching range, advantageously converted into binary signals. This means that the two sensor output signals are digitized with 1 or more bit resolution, knowing the shape of the characteristic curve.

The evaluation circuit for determining this linear location information perpendicular to the direction of rotation level requires, for example, four triggers with switching thresholds at approximately half the amplitude, each bridge being provided with a positive and a negative switching threshold. An OR gate combination of the output signals gives a high signal as soon as the magnitude of one of the two output voltages exceeds the trigger threshold.

As a result, the invention creates an inexpensive, contactless, electronic rotary switch with an integrated push-button function.

To actuate the button function, the rotary knob rotating the magnet wheel itself or a separate button embedded in this rotary knob can serve as actuation means, the distance between the magnet wheel and sensor being either increased or decreased when the button is pressed. If the rotary movement positions are only to be forwarded in only one of the two switching positions, which switching position would correspond to that with a small distance between the magnet wheel and the sensor, a rotary switch with anti-rotation lock is implemented when the distance is reduced at the push of a button, in which the rotary switch function only presses of the rotary knob responds. In contrast, a rotary switch with confirmation function is implemented in the event of an increase in the distance at the push of a button.

According to the invention, however, a plurality of switching ranges can be provided per output signal with a plurality of switching thresholds for the linear displacement of the pole wheel to the sensor. Such a choice of function depends then on the resolving power and the course of the sine or cosine curve. In a case with a multiple linear switching range, the output voltage amplitudes are divided into several stages, the number of stages multiplied by the rotary switching stages giving the total number of switching positions to be assumed by means of the rotary switch. The sensor signals can then be digitized with a resolution higher than 1 bit in order to evaluate the characteristic from the digitized result.

The invention is explained in more detail below with the aid of a rotary switch exemplary embodiment with an additional two-stage switching function with the aid of the attached drawing. In this shows:

1 schematically shows the arrangement of individual components of the rotary switch according to the invention for the various push-button rotary switch variants;

2 shows two periodic output signals from the sensor;

3 is a graph illustrating the output amplitude of a magnetoresistive sensor as a function of the magnetic field strength at the sensor location;

4 is an exemplary graph showing the field strength and sensor amplitude of the magnetoresistive sensor as a function of the distance between the magnet wheel and the sensor;

FIG. 5 shows an exemplary graph in which the output characteristic curves of the magnetoresistive sensor are shown with the magnet wheel sensor at a small distance; FIG.

Fig. 6 is an exemplary graph in which the output characteristics of magnetoresistive sensor at a medium distance magnet wheel sensor are shown;

FIG. 7 shows an exemplary graph in which the output characteristic curves of the magnetoresistive sensor are shown with the magnet wheel sensor at a large distance; FIG.

8 shows a circuit diagram of a circuit arrangement;

FIG. 9 shows an exemplary representation of the signal curve in the evaluation circuit for a characteristic curve according to FIG. 5;

10 shows an exemplary representation of the signal curve in the evaluation circuit for a characteristic curve according to FIG. 6;

11 shows an exemplary representation of the signal curve in the evaluation circuit for a characteristic curve according to FIG. 7.

Fig. 12 Analog evaluation.

Fig. 1 shows schematically the arrangement of individual components of the rotary switch. With a rotary knob 4 of the rotary switch, a magnet wheel 2 (not shown) which is equipped with magnetized poles (not shown) can be rotated about a rotation axis 3 and displaced linearly according to arrow v. By turning the pole wheel, the poles pass through the measuring range of a magnetoresistive sensor 1. This sensor detects the impulses of the field strength change and, as a result, outputs a periodic output signal at two sensor outputs. In the present case, the first signal output by the magnetoresistive sensor is a periodic cosine signal, while a periodic sine signal is tapped at the second output. As shown in FIG. 2, with a complete phase sweep of 360 ° of the signal, both signals carry out a complete voltage sweep from 0 to the positive and negative amplitudes. The angle scaling given here on the ordinate axis therefore refers to the phase position of the signal and not to the angular position of the pole wheel.

In the present case, the two signals have a constant phase shift of ^" Α period, ie π / 2. This constant phase shift means that any angular position after counting the detected pulses and the determined direction of rotation is characterized by comparing the two signal voltages.

3 shows the output signal amplitude as a function of the magnetic field strength. As shown in this figure, the output signal amplitude also decreases with decreasing field strength at the sensor location. It can also be seen that the signal drop increases rapidly above a certain limit of the field strength. If this relationship is combined with the course of the field strength on a pole wheel as a function of the distance from the sensor to the pole wheel, an exemplary representation of the dependence of the sensor output signal amplitude on the distance between the sensor and the pole wheel is shown in FIG.

As can be seen in FIG. 4, at short distances from the magnet wheel to the sensor there is a zone in which the signal amplitude is very large with only a small spatial dependence. From a certain distance, the signal amplitude then drops steeply - as already mentioned above. In practice, harmonics in the sine or cosine curve, which lead to severe deformations of the characteristic curve, often occur at this limit. The generation of a usable output signal for the pole count is, however, only impaired by the curve deformation or the decrease in amplitude at very low field strengths. In order to implement a two-stage switching function in addition to determining the rotational angle position, the distance of the pole wheel to the sensor is measured via the signal strength according to the invention. In order to determine whether the distance between the magnet wheel sensor and the distance between them is small, based on the two output signals alone, the relationship in the present case with a phase shift of VA period becomes:

SUI Λ; = COS Λ; for x = -

4 used between sine and cosine, whereby

π sm = A

2 and π A sm— = -τ = 4 2 with A = magnitude of the amplitude.

In the case of pure sine or cosine-shaped characteristic curves, the magnitude of the output voltage of at least one output for each phase angle

A greater than - _j = - because at the intersection of the graphs when the sine

V2 curve the cosine curve rises and vice versa (see Fig. 2).

With reference to FIG. 5, an example of the characteristic curve of the output signals of the sensor with a small distance between the magnet wheel and the sensor is shown.

Now, as in the present case, two threshold switches are provided per output channel, one switching threshold + S in the positive voltage range and the other switching threshold -S in the negative

A voltage range and below this limit ISI <- =, then

V2, it can be determined that these switching thresholds have been undershot without losing the information about the angle of rotation position. This is wave-free characteristic as soon as the signal amplitude is greater than that

If, as shown in FIG. 6, the signal amplitude A is in the range S≤A≤S - -> / 2, the pulse state depends on the respective phase angle. Because in this range the signal value only exceeds the value S-2 at certain phase angles θ (for example 0 = 0). Thus, at certain phase angles, the trigger threshold is below one amplitude, but not under both amplitudes. In contrast, the trigger threshold of both amplitudes is not reached at other phase angles (see also digital 1-bit signal in FIG. 10). This area should only be run briefly when the button is pressed or released. The end points of the sensor-magnet wheel movement must be in the outside areas with clearly defined switching states to ensure functional safety.

If, as shown in FIG. 7, the signal amplitudes drop below the threshold value S of the threshold switches as a result of an increase in the magnet wheel sensor distance, no threshold value switch signals that the switching threshold has been exceeded for any phase angle. The forwarding of the rotational angle positions, which can still be measured in this state, are then not forwarded according to the present embodiment by the switching function after an interruption.

When choosing the type of sensor to be used, care must be taken that the sensor at the lower limit of the undefined switching range still generates a perfect output signal that is of sufficient quality for reliable counting and direction of rotation pulse generation.

8 shows the possible circuit arrangement for determining whether the magnitude of the output voltage of one of the two sensor outputs exceeds a predetermined limit or whether the magnitude of the output voltage for both sensor outputs is below the specified limit at the same time.

The evaluation circuit consists of two parts. One part contains two Schmitt triggers with a switching threshold at OmV / V, which generate a counting pulse signal and a direction of rotation signal for a digital counter from the two bridge signals.

The second part of the circuit requires four Schmitt triggers with which the switching thresholds are set. Each magnetoresistive bridge has a trigger threshold set in the positive range and a trigger threshold in the negative range. An OR operation is connected between the detected trigger signals for the amplitudes, so that it is always determined when the magnitude of one of the two output signals exceeds the trigger threshold. If the amounts of both output signals are below the threshold, no high signal is passed on via the OR link.

FIGS. 9, 10 and 11 show the signals which can be determined in the switching arrangement of FIG. 8. FIG. 9 shows the signals at points A to G of a characteristic curve according to FIG. 5 output by the sensor. Correspondingly, FIG. 10 shows a signal series A to G based on a characteristic curve shown in FIG. 6, while FIG. 11 shows a signal series A to G according to a characteristic curve of FIG. 7.

The signals A to G are in a digitized form with 1-bit resolution, the signal

A the sine signal B the cosine signal

C the threshold value exceeded + S of the sine signal

D the threshold value exceeded -S of the sine signal the overshoot + S of the cosine signal, the overshoot -S - the cosine signal and the undershoot of one of the two output signals

equivalent.

As can be seen from FIG. 10, the digital 1-bit signal G at certain phase angles of the signal shows that at these angles the trigger threshold is undershot by one signal, but not by both signals. In contrast, the trigger threshold of both signals is not reached at other phase angles. As mentioned above, this area should only be run when the button is pressed or released and for as short a time as possible. The end points of the sensor-magnet wheel movement must be in the outside areas with clearly defined switching states to ensure functional safety.

Finally, it should be emphasized that the sensor signals can be evaluated both in analog and in the corresponding example above in digitized form. This means that even with an analog evaluation for exceeding or falling below the threshold value, subsequent digitization with a resolution of 1 bit or more leads to a switching function of the rotary switch via the distance between the pole wheel sensor.

In order to make the switching point more reproducible or to record the sensor-pole wheel distance with a resolution greater than 1 bit, it is advisable to reduce the undefined switching range. This includes determining the sensor signal amplitude independently of the respective position of the phase angle. If pure sinusoidal or cosine-shaped signals are assumed, the relationship A = ψ _ + U _QS can be used for this become. The implementation of this amplitude determination in terms of circuitry and the subsequent digitization can take place digitally both analog (FIG. 12) and after prior digitization of the sensor signal. A digital evaluation has the additional advantage of being able to take deviations from the sin shape, offset errors, temperature influences, etc. into account.

Claims

claims:

1. Contactless transmitter, which has a signal transmitter unit with signal transmitters and a signal pickup unit and, upon detection of a signal emitted by the signal transmitter to the signal pickup unit, permits an expansion of the switching function by signal analysis of the signal.

2. Encoder according to claim 1, with a rotary switch, the signal transmitter unit is a magnet wheel (2) with n-magnetic poles as the signal transmitter and the signal pick-up unit is a magnetic field sensor (1).

3. Encoder according to claim 2, wherein the signal strength of the signal measured by the signal pick-up unit defines a switching range which is a function of the distance from the magnet wheel (2) to the magnetic field.

Sensor (1) is set.

4. Encoder according to claim 2 or 3, wherein the sensor has a first output signal output at which the sensor outputs a sinusoidal output signal in a first approximation, and a second output signal output at which the sensor cosines a first approximation. outputs a nut-shaped output signal, which output signals are constantly phase-shifted from one another.

5. Encoder according to claim 4, wherein the two output signals are constantly shifted from one another with a phase shift of a% period.

6. Encoder according to claim 4 or 5, wherein an analog-digital converter is provided with which the two output signals of the sensor are digitized.

7. Encoder according to one of claims 4 to 6, wherein a threshold switching unit is provided with which the two output signals are each converted into binary sensor signals with a constant amplitude and the rotational position of the pole wheel is determined from the edge change of the binary sensor signals.

8. Encoder according to one of claims 4 to 7, wherein a threshold switch unit is provided from threshold switches which define a switching threshold range for each output signal, with a measurement of the two amplitudes of the output signal voltages of the

Sensor depending on the distance between the pulse generator unit to the pulse pickup unit in a radial or axial movement direction to the axis of rotation of the rotary switch an exceeding or falling below the threshold values of the two output signals is determined.

9. Encoder according to claim 8, wherein a threshold value range is defined by the threshold switches per output signal, which is limited by the amount of the output signal voltages and down by the amount of a predetermined voltage value of the output signal voltages, below which a reliable determination of the rotational position of the magnet wheel the characteristic is still possible.

10. Encoder according to claim 9, wherein a circuit device is provided with which the information about the distance of the signal generator unit from the pulse pick-up unit is converted into a binary 1-bit switching signal which gives the rotary switch a switching stage function "on-off".

11. The encoder of claim 10, wherein the switching stage switches a forwarding or interruption of the rotational position signal.

12. Encoder according to one of claims 4 to 7, wherein a switching threshold unit with a plurality of switching thresholds are provided which define a plurality of switching threshold ranges per output signal, the lowest switching threshold range by the amount of a predetermined

Voltage value of the output signal voltages is limited below which a reliable determination of the rotational position of the magnet wheel from the characteristic curve is still possible, the distance between the magnet wheel (2) and sensor (1) being determined with a resolution of more than 1 bit.

13. Use of a rotary sensor consisting of a pole wheel with n-magnetic poles and a magnetoresistive sensor as a rotary switch unit, the switching stages of which are defined by the pulse count of the pulses generated by the poles.