DE19520299A1 - Detection unit for identifying position of movable body e.g. shaft in motor vehicle - Google Patents

Abstract

The detector has a two sensor system (10,11) which deliver their output signals to a common microcontroller (13) for evaluation. The first system includes a code carrier, which has a first track with a multiple oaf same type markings, which are arranged at equal spacing from each other. A second track is provided with at least one reference marking. A sensor element is provided with at least two pick-ups, which are allocated to the individual tracks. The second sensor system has at least one marking element, which stands in engagement with the body e.g. a shaft (12), the rotational angle ( alpha ) of which, is to be determined, and with a pick-up, which is allocated to the marking element. The first sensor system is an optical sensor system and the second sensor system works according to the magnetic-Hall principle.

Description

State of the art

The invention is based on a device for position detection according to the genus of the main claim.

It is known that for position detection or for angle detection tion, for example to detect the angular position of a Shaft in a motor vehicle, sensor systems who used those that include a transducer, one with the shaft in Connected code disc scans and an output si gnal, which contains information that allows to recognize the position of the shaft.

Such sensor systems work according to different physi procedures, as examples of common sensor principles May be mentioned: Hall sensors, inductive sensors on vertebrae current base, potentiometer, capacitive sensors and magne toresistive sensors. These sensors generally work reliable and wear-free. In motor vehicles with the help of such sensors, for example, the pedal value posi tion with an electronic accelerator pedal, the throttle valves position with an e-gas actuator, the brake pedal position at electronic brake pedals or the position of the cure bel- or camshaft determined.  

An example of devices or methods for position detection voltage is given in DE-OS 42 43 778. Doing so Device described in which a code carrier a first Has a track with a large number of similar markings and a second track with distinguishable markings or same markings at different distances. These Markings are scanned by at least two sensors continuous The code carrier and the two sensors form one Sensor system, the output signals in a subsequent Evaluation device are evaluated to recognize the Location of the code carrier, for example to identify a Angular position. As examples of using a sol Chen device is the determination of the steering wheel angle or the throttle valve position in an internal combustion engine specified.

The object of the present invention is an improvement the device known from DE-OS 42 43 778 for location recognition. The problem is solved by the in claim 1 specified device for position detection.

Advantages of the invention

The inventive device for position detection with the Features of claim 1 has the advantage that particularly reliable and accurate measurements can be carried out NEN, which is particularly advantageous that a redundant System in place in the event of a system failure still provides sufficient information. It is white further advantageous that the claimed system touch and works wear-free and without extensive testing and Matching operations can be used, which is far independently calibrated. It is also advantageous  that the specified system has no temperature response and none Exhibits drift phenomena.

These benefits are achieved by using a combination of two independent measuring systems into one System is carried out, the combination being such that the disadvantages of the individual systems disappear and the Advantages of the individual systems are used. It will used two sensor systems, which according to differ physical principles. Be linked the two sensor systems with the help of a microcontroller, which is adaptable to application-specific modifications.

Further advantages of the invention are shown with the help of the Characteristics specified achieved. It is particularly advantageous that the first sensor system an opti cal sensor system is that with light-emitting elements works over a transducer disc with translucent Interact with the transducers and the second Sensor system is a magnetic Hall system in which a Hallele ment interacts as a sensor with a magnet.

The claimed device can advantageously be used device for position detection to determine the pedal value position, the throttle plate position, the brake pedal position, the Steering angle determination or in connection with an illuminated sign use tenregulierung in motor vehicles, because the there required reliable functioning is ensured.

drawing

An embodiment of the invention is shown in the drawing and is explained in more detail in the following description. In this case, 2 is a waveform for the sample of Figure 1 showing in detail Fig., The overall system in a simplified illustration, Fig. An embodiment of the first sensor system, Fig. 3 is an explanatory drawing of the optical system of FIG. 2 and FIG. 4. 3, in Fig. 5 is a waveform for the optical system of FIG. 2 provides Darge.

FIG. 6 shows an example of a magnetic Hall system which forms the second sensor system, in FIG. 7 a curve of the Hall voltage is plotted against an angle of rotation. In Fig. 8, the structural design of the overall system is Darge and Fig. 9 shows the block diagram for a redundant embodiment with two microcontrollers. A further embodiment of the sensor systems is shown in FIG .

description

In Fig. 1 an embodiment of the inventive device for position detection is shown schematically. This example shows the basic principle, which is that two completely different sensor systems 10 , 11 are combined to form a common device for position detection, the properties of both sensor systems being linked to one another in such a way that the disadvantages of the individual sensor systems are combined not noticeable and the advantages of the individual sensor systems are combined to form a low-cost overall system.

The sensor systems 10 , 11 are arranged so that they can determine the angle of rotation α of a shaft 12 . The sensor systems 10 , 11 are connected via connections V1, V2, V3, V4 to the microcontroller 13 , which uses the output signals of the two sensor systems and provides an output signal OUT which represents the angle α to be determined.

The embodiment of FIG. 1 is of course not limited to the evaluation of an angle of rotation α of a shaft 12 , but can also be used in conjunction with a linear movement. Either the sensors can be fixed and the code disk or the magnets etc. can be connected to the movable body or vice versa.

In Fig. 2 an example of the first sensor system is given, it is an optical sensor system that is already known from DE-OS 42 43 778. In this system, a code disc 14 is connected to the shaft 12 , whose angle of rotation α is to be determined. The code disk has a first track 15 , with a plurality of similar marks 16 , all of which have the identical distance d. A second track 17 , which represents the reference track, has similar marks 18 a to 18 i, the spacing of which is an integer multiple of the distance d1, this integer multiple of 1 (between the marks 18 a and 18 b) to 8 (between the brands 18 i and 18 a) runs. The distance between the mark 18 b and 18 c is labeled d2, the distance between 18 c and 18 d is labeled d3, etc.

The code disc 14 together with the sensor 19 forms the sensor system 10 . The sensor system 10 comprises a light-emitting element which is arranged on one side of the translucent code disc, while the sensor 19 is on the other side and the marks 16 and 18 a to 18 i are formed as translucent locations or breakthroughs.

The sensor 19 outputs a characteristic output signal as a function of the brightness regi strated by it, that is, depending on whether there is an opening or the opaque sensor disk between the light-emitting element and the sensor in question. This output signal is fed to the microcontroller 13 , which usually includes suitable counting and storage means and determines the measured angular position.

The sensor 19 can have, for example, three light-sensitive elements, for example photodiodes, the first and the second photodiode being assigned to the track 15 and delivering the signals A and B, respectively. The third photodiode is assigned on track 17 and supplies signal I. The resulting signal curve is shown in FIG. 4.

Such a sensor 19 , in which, however, six photodiodes are present, is known from a company brochure from HP with the name "Three Channel Optical Incremental Encoder Modules". It is a sensor that internally generates a total of six signals, whereby two signals for A, B and I are obtained, which are compared with each other, so that ultimately the difference between two signals A or two signals for light / dark detection B or two signals I can be used, which compensates for an age-related change in sensitivity of the photodiodes.

A sensor operating according to another physical principle can also be used as the sensor 19 , which emits at least two signals A and I, that is to say one signal for each track 15 , 17 . It is then necessary to adjust the encoder disc 14 in a suitable manner. With a sensor that only emits two signals, an evaluation is only possible if there is no change in the direction of rotation. A defined zero position is determined in the system described with the aid of the reference marks 18 a to 18 i.

In a further embodiment, the track 19 has only a single reference mark, which is used to determine the zero position.

Furthermore, an arrangement as outlined in FIG. 10 can be used as the sensor 19 . Signals A, B, I are again generated, magnetic Hall barriers 48 , 49 , 50 being used in conjunction with a magnetically conductive diaphragm wheel 51 with a number of angular marks. The distribution of the magnetic flux results depending on the angular position of the diaphragm wheel. The arrangement corresponds in principle to the arrangement of the optical system according to FIG. 2, the optical sensors having to be replaced by Hall barriers 48 , 49 , 50 .

The direction of rotation is also detected in the system according to FIG. 10 with the Hall barriers or Hall sensors set by half an angular mark distance.

The sensor system 10 , that is to say the optical scanning system, is located in a common fork-shaped housing; the exact arrangement can be found, for example, in FIG. 8. As shown in FIG. 3, a light emitting diode 20 , which is supplied with voltage via the inputs 1 , 4 and the resistor 33 , is on one side and the receiver array on the other side of the fork. So that only a light-centering diode 20 is required as the light source, its light is parallelized with a correspondingly designed lens 27 . The three receiver systems with the photodiodes 21 to 26 are integrated with the associated amplifier circuits 28 , 29 , 30 in a common chip 31 , which also includes the evaluation μC 32 . At the outputs 2 , 3 , 5 of this chip there are three pulse sequences available: Channel A and B represent the pulses that correspond to the change in angle, channel I supplies the reference point or the zero position of the code disk 14 . Information about the direction of rotation of the disk can be obtained from signals A and B, which are phase-shifted by 90 °.

In FIG. 4, the signals A, B and α plotted as voltage signals over an angle I are. Some of the routes required for signal processing are identified with the appropriate names. Fig. 4 is in the rest gene like Fig. 2, 3, 4, 5 part of DE-OS 42 43 778, which provides more detailed information on the optical sensor system according to Fig. 2.

Together with the index marking and the direction of rotation detection, the arrangement according to FIG. 2 offers all the prerequisites for measuring an angle of rotation α with a specific resolution given by the part of the code disk 14 . With 360 holes per disc and taking advantage of the possibility of quadrupling the pulse, an angular resolution of 0.25 ° can be achieved in the entire rotation angle range of the disc. This resolution corresponds to the measurement accuracy of the sensor system 10 because of the functional principle, it is independent of the area and applies over the entire temperature range.

This property represents the essential advantage of the sensor system 10. A disadvantage of this principle is the fact that it is an incremental encoder, the information of which is not immediately valid when the sensor is switched on. The index mark of the sensor must first be reached by an action before the sensor signal is valid. In other words, the angular position can only be determined continuously after the disk has rotated through a certain angle.

Together with the second sensor system 11 , which is constructed, for example, as a magnetic Hall system, the device claimed for position detection results.

The magnetic Hall system used as sensor system 11 , which is shown in Fig. 6, is designed so that the Hall sensor 34 reacts to the angle of rotation α of the magnetic field or the shaft. In the exemplary embodiment according to FIG. 6, the magnetic field is formed by a double magnet 35 , 36 which, on the other hand, is firmly connected to the axis of rotation of the shaft 12 .

The stationary Hall sensor with its active surface, that is to say the active Hall element 37 , is perpendicular to this magnetic field. The magnetic field rotating with the axis of rotation causes a sinusoidal voltage change in the Hall sensor over the angular range of 360 °. In the embodiment, a range of use of the angle sensor of a maximum of 120 ° is neces sary, it is therefore possible to find an area within the sine function that can be used with sufficient accuracy by conventional linearization methods for angle measurement.

A typical voltage curve of the output voltage of the Hall element UH over the angle α is shown in FIG. 7 Darge. By using Hall elements with integrated preamplification, an output level can be realized that can be processed directly by a microcontroller.

If only one is used Magnet Hall sensors would have the following disadvantages: It would be a dependency of the output signal on the magnet field strength exists, caused by the distance between Magnet and Hall sensor as well as certain magnetic properties by the dependence of the output voltage on the Hall element properties, for example offset, temperature response, Gain factor, a non-linearity of the measurement method  due to the sinusoidal shape of the signal voltage the angle of rotation α.

However, the disadvantages of the two individual systems 10 and 11 can be completely avoided by combining the sensor systems 10 and 11 . The result is a sensor system that meets the requirements of an angle measuring system in an almost ideal way.

The linkage of the two sensor systems is carried out with the aid of a microcontroller 13 according to FIG. 2. If true redundancy should be required, an evaluation by means of two microcontrollers 41 , 42 can be realized with an arrangement according to FIG. 9 described in more detail later. The microcontroller or microcontrollers have the task of detecting the digital output signals of the optical incremental sensor 10 and converting them into an output value corresponding to the angle of rotation α. The voltage signal of the Hall magnet sensor 11 is detected by an analog-digital converter of the microcontroller and converted via an algorithm into an output value corresponding to the angle of rotation.

The program of the microcontroller (s) ensures that the measured values of the sensor systems 10 and 11 are linked in such a way that an output signal is produced in the entirety of the solution, which overall meets the requirements for a precise angle measuring system. The algorithm required for this consists of two parts, which are described as follows:

In part 1 of the algorithm, the concerns of manufacturing of the sensor with the associated adjustment steps wrote. In this part of the algorithm the characteristic of the magnetic Hall system using the optical incremental sensors linearized. The optical system serves as  Basis with sufficient accuracy, based on this A lineari is used to compare values in an external computer generation function or a table, which then the Microcontroller is passed. With the help of this linearization The function or table can be used for the magnetic Hall sensor sufficient accuracy can be achieved. The correction the temperature response of the magnet Hall system is possible but not required for the intended applications Lich. The self-calibration of the sensor system can be achieved that the previously strongly non-linear Magnet Hall system approximately the measurement accuracy of the opti has encoders.

Part 2 of the microcontroller algorithm is for that actual measurement of the sensor responsible. It will be there assumed that when the sensor is turned on optical encoder has not yet recognized its reference point Has. In this case it is not possible to use the optical to use incremental system for angle measurement. Of the In this case, the algorithm causes the Analog-to-digital converter of the analog signal of the Magnet Hall system out as a measured value for the angle of rotation α will give. This is the case until the code has moved into a position in which the Reference mark of the optically incremental system recognized becomes. From this moment on, the algorithm ensures that the angle generated by the optical system, the one has higher accuracy than the measured angle of rotation is given.

For security reasons, the signals of the Magnet Hall system and the optical incremental system continuously compared with each other, so that errors are clear can be detected. In this way, the sen  soranordnung a high degree of intrinsic safety and it results the possibility of recognizing incorrectly plausible values.

If one of the sensor systems 10 , 11 fails during operation, the intact sensor system alone can take over the measuring function with restricted parameters. Redundancy is therefore possible in safety-critical systems.

By using one or two microcontrollers in the sensor there is the possibility of a digital interface between the sensor and a subsequent evaluation device, e.g. B. to implement a microcontroller, for example a CAN, UART, PWM interface. Then it's a pro easy adaptation to a wide variety of evaluation systems possible.

A constructive implementation of the entire device for position detection is outlined in FIG. 8. It consists of a lower housing part 38 in which there is a shaft 12 which is rotatably mounted in a bushing 39 and which in turn is connected to the unit, that is to say e.g. B. the shaft is connected, whose angle of rotation α is to be measured. Fixed to this shaft 12 is the code disk 14 , which is part of the optical incremental encoder, that is to say the sensor system 10 . The number of markings on the code disk is determined by the required resolution of the angle measuring system.

As an example, a disc with 360 marks (Holes) are inserted, creating an angular resolution of 0.25 ° can be reached. The number of marks can be significant Lich selected higher if this should be necessary te. With more than 1000 markings there is an angular resolution of 0.1 ° possible. Those arranged in the second lane Index marks serve as a reference point for the incremental system. When using multiple index marks, the  Incremental system initialize faster, moreover there is the possibility, when recognizing index marks, of to check and verify the measured value determined in each case ren.

On the lower housing part 38 there is the sensor belonging to Codeschei, which comprises the plate in the form of a fork, with the light-emitting diode with lens for parallelizing the light on the top of the fork and a photodiode array for generating the two by 90 ° on the underside of the fork pulse sequences A and B shifted against each other and for recognizing the index marks I.

The magnet arrangement, which in turn consists of two individual magnets 35 , 36, is firmly connected to the shaft 12 . The single magnets are paired with opposite poles, so that there is a typical field curve, as shown in Fig. 7. The central axis of the magnet arrangement is aligned with the central axis of the shaft 12 .

The Hall sensor 34 is located at a distance a from the magnet arrangement, and its active surface 37 stands in the magnetic field generated by the magnet arrangement. The Hall sensor itself consists of the Hall element and an integrated preamplifier, which amplifies the Hall voltage so that the Hall voltage change caused by the rotation of the magnet is in a range of about 1-4 volts. This voltage can then be applied directly to the input of the Mikrocon troller 13 belonging to the analog-to-digital converter.

The Hall sensor itself is on a wiring carrier 40 , which is used in the lower part of the housing. The microcontroller 13 belonging to the system with all the components required for its function is also located on the wiring support 40 . These components, which are not shown in the drawing, include at least one fixed voltage regulator, a crystal for generating the vibrations, various capacitors and resistors, which are not shown. A lid 47 closes the entire system.

A block diagram of a possible circuit is shown in Fig. 9, for a redundant solution with two Mikrocon trollers 41 , 42 and two analog-digital converters 43 , 44 and two CAN interfaces 45 , 46 . The sensor systems 10 , 11 and the two microcontrollers 41 , 42 are connected to one another in a suitable manner.

Instead of a sensor consisting of an optical and a Magnet Hall system can be single sensor systems that work according to other physical principles will. The prerequisite is that the two Sen sor systems work according to different principles. On Instead of the optical system, for example, a magnet system are used in which a ferro magnetic disc is used with inductive on is sampled. Ent can be used as markings no slits or teeth or areas of other material be used.

Claims (14)

1. A device for detecting the position of a movable body pers, with a first sensor system that works according to a first physical principle and emits a signal dependent on the position to be determined, characterized in that a second sensor system is present, which according to a second physical principle works and emits a signal dependent on the position to be determined and an evaluation device is available which jointly evaluates the output signals of the first and second sensor systems. 2. Device according to claim 1, characterized in that the first system comprises a code carrier having a first Track with a variety of similar marks that are arranged at the same distance from each other, includes and has a second track with at least one reference mark and a sensor element with at least two sensors are assigned to the individual tracks. 3. Device according to claim 1 or 2, characterized net that the second sensor system at least one marker Has element that determines the position of the body communicates with a transducer who is assigned to the marking element. 4. Device according to one of the preceding claims, characterized in that either the code carrier as well  the marking element is movable and the two sensors systems are fixed or the code carrier is fixed and the at the sensor systems are movable, the movable part on the body whose position is to be determined is ordered. 5. Device according to one of the preceding claims, characterized in that the first sensor system is an opti cal sensor system and the second sensor system after Magnet Hall principle works. 6. Device according to claim 5, characterized in that the code carrier is opaque and the markings are designed as slots or holes that the light-emitting ting element arranged on one side of the code carrier and the transducers are on the other side. 7. Device according to claim 6, characterized in that the light emitting element is a light emitting diode and the Sensor photocells, two photocells each one transducer are combined. 8. Device according to one of the preceding claims, characterized characterized in that the second sensor system is a Hall sensor with an active Hall element comprising at least two Scans magnetic elements in conjunction with the code carrier stand. 9. Device according to one of the preceding claims, characterized in that the code carrier is a code disk which is connected to a shaft, the angle of which position (α) is to be determined. 10. Device according to one of the preceding claims, characterized in that two interacting microcon  trollers are provided with each of the two sensors systems related and a common exit provide a signal that corresponds to the size to be measured. 11. Device according to one of claims 1, 2 or 3, characterized in that the first sensor system after works on a magnetic principle and the code disc a material with predefinable magnetic properties is manufactured and the brands as areas with other magne table properties are formed and as sensor elements te inductive sensors are used. 12. Device according to one of the preceding claims, characterized in that the evaluation device either comprises a microcontroller that consists of both sensor systems evaluates or at least two microcontrollers, both Evaluate sensor systems and connect them to each other stand. 13. The device according to claim 12, characterized in that the microcontrollers include interfaces to the expected requirements are adaptable. 14. Device according to one of the preceding claims, characterized in that it is used to identify a pedal value position or a throttle valve position or a Brake pedal position or a steering angle or steering wheel win kels is used in a vehicle.