DESCRIPTION

Sensor for Detecting a Moving Direction

Field of invention

The present invention relates to the field of detecting a moving direction and a vibration.

Technical background

The Document US 20050007103 Al shows a sensor assembly and method for sensing direction of rotation and/or position of an object. The sensor assembly includes a target wheel.

Summary of the Invention

It is an object of the present invention to provide a sensor and a method for detecting a moving direction, which leads to quick results. Especially there is a need for a method to determine the moving direction in order to detect vibration.

This need may be met by a sensor, and a method according to the independent claims. Further exemplary embodiments are disclosed in the dependent claims.

According to an exemplary embodiment, a sensor for detecting a moving direction comprises a first voltage divider with a first output voltage, a second voltage divider with a second output voltage, whereas a voltage divider comprises a magnetoresistive element, a subtractor with a subtracting result depending on the subtraction of the first and the second output voltage, an adder with an adding result depending on the addition of the first and the second output voltage, a sampler with a

sampling result, which is obtained by sampling the adding result depending on the subtracting result and a holder for holding the sampling result.

An exemplary aspect of an exemplary embodiment of the invention may be seen in that the sensor comprises a holder, which has a hysteresis.

According to an exemplary embodiment, a method for detecting a moving direction comprises dividing a voltage with a first voltage divider, which leads to a first output voltage, dividing a voltage with a second voltage divider, which leads to a second output voltage, whereas a voltage divider comprises a magnetoresistive element, subtracting the first and the second output voltage, which leads to a subtracting result, adding the first and the second output voltage, which leads to an adding result, sampling the adding result depending on the subtracting result, which leads to a sampling result and holding the sampling result.

According to an exemplary embodiment, a method will be provided, whereas the sampling takes place at a zero crossing of the subtracting result.

According to an exemplary embodiment, a method comprises determining a change of the adding result in comparison with the sampling result.

According to an exemplary embodiment, a method comprises: determining a change of the adding result in comparison with a threshold, whereas the threshold depends on the sampling result.

According to an exemplary embodiment, a method comprises: determining a second change of the adding result after a period of the subtracting result.

According to an aspect of the invention, there is provided a method, which comprises determining the vibration by the relationship of the change and the second change.

According to another exemplary embodiment, a method comprises: defining vibration, if the change has a different algebraic sign than the second change.

According to another exemplary embodiment, a method is provided, which comprises: determining a valid movement by the relationship of the change and the second change.

According to another exemplary embodiment, a method comprises: defining the valid movement, if the change has the same algebraic sign as the second change.

Brief description of the drawings

Exemplary embodiments of the present invention will be described in the following, with reference to the following drawings.

Fig. 1 shows two graphs, whereas one graph is the result of a subtraction of two voltages and the other graph is the result of an addition of these two voltages;

Fig. 2 shows two graphs, whereas one graph is the result of a subtraction of two voltages and the other graph is the result of an addition of two voltages;

Fig.3 shows three graphs, whereas the top graph is the subtraction of two voltages, the middle graph shows a substraction of voltages Ul and U2 (speed signal) and the lowest graph shows an addition of two voltages;

Fig. 4 shows a schematic illustration according to an exemplary embodiment;

Fig. 5 shows a flowchart according to an exemplary embodiment;

Fig. 6 shows a flowchart of a further exemplary embodiment;

Fig. 7 shows a flowchart of another exemplary embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

The illustration in the drawings is schematically.

Fig. 4 shows two voltage dividers 14 and 15. The voltage divider 14 comprises two elements 16 and 17 and the voltage divider 15 comprises also two elements 18 and 19. At least one of the elements 16, 17, 18 and 19 is a magnetoresistive element. The other elements are usually normal resistors. These elements 16, 17, 18 and 19 are arranged in such a way, that the direction of a movement of a target wheel as well as the speed thereof can be detected. The arrangement of the elements 16, 17, 18 and 19 in order to fulfil the above functions as well as the target wheel itself is state of the art. Therefore, the person skilled in the art is able to arrange these elements adequately. The voltage dividers 14 and 15 are supplied by the supply voltage UB. On the other side, the voltage dividers 14, 15 have contact to mass or they are grounded. The point between the element 16 and 17 has one voltage, which is an output voltage Ul of the voltage divider 14. The point between the elements 18 and 19 has a second voltage U2, which is the output voltage of the voltage divider 15. These output voltages Ul and U2 are subtracted in the device 20 and added in the device 21. With the help of the results of these two devices 20 and 21 the direction of the movement of the target wheel can be determined. The result of the device 20 alone can be used to find out the speed of the target wheel.

Fig. 1 shows two graphs 1 and 3, whereas the upper graph 1 is the result of the subtraction of two output voltages Ul and U2 and the lower graph 3 is the result of the addition of these two output voltages Ul and U2. The X direction shows the value of the angle. These graphs 1, 3 show exemplary situations of a target wheel,

therefore on the X direction there is shown the angle of the target wheel. It is also depicted a line 2, which shows that at that value of angle at which the upper graph 1 crosses the zero line the lower graph 3 has a peak.

Fig. 2 illustrates two graphs 4 and 5, whereas the upper graph 4 shows the result of the substraction of the two voltages Ul and U2 and the lower graph shows the result of the addition of the two voltages Ul and U2. There is also a line 6, which leads from the point at where the upper graph 4 crosses the zero line to the lower graph 5. This line 6 illustrates that at the same time (at the same angle) at which the subtraction of the two voltages Ul and U2 crosses the zero line there is the lowest point of the result of the addition of the voltages Ul and U2. The graph 5 there has a valley.

Fig. 1 shows the situation when the target wheel is moving (rotating) in one direction and Fig. 2 shows the situation when the target wheel is moving (rotating) in the other direction. Therefore, it is possible to determine in which direction the target wheel is moving (rotating) with the help of the comparison of these two graphs 1, 3 and 4, 5, respectively. Therefore, there is a shifting phase by plus or minus 90° of the graph 3 or 5 in comparison to the graph 1, 4 (substraction of voltages Ul and U2 (speed signal)) depending on the direction of rotation (movement). Therefore, to be able to determine the direction of the target wheel, it is necessary to be able to discover the peak points and the valley points of the addition of the voltages Ul and U2. The obtained direction signal, the addition of Ul and U2 has however an offset in the range of the supply voltage UB of the voltage dividers 14, 15. For direction detection, this offset has to be compensated first. With current magnetoresistive speed sensors like the OH22X, the offset compensation of the direction signal is done by tracking the maximum and minimum amplitudes and compensating the offset with a digital logic and DA-converter. This way of signal conditioning requires high effort, which is avoided by the invention. Additionally, the offset compensation method requires several signal periods in order to determine the direction of movement of the target wheel, which causes problems in detection of target wheel vibrations.

Fig. 3 illustrates three graphs 7, 8 and 10. The first graph 7 is the depiction of the voltage resulting as the subtraction of the two output voltages Ul and U2. This resulting voltage is rectified into a half- wave signal and then transformed into a square form signal 8. The graph 8 illustrates a voltage, which can directly used as a signal for determining the speed of the target wheel. The frequency of the substraction of voltages Ul and U2 (speed signal) corresponds to the speed of the movement (rotation) of the target wheel. The lower graph shows the addition of the two voltages Ul and U2. In the moment of the change of the substraction of voltages Ul and U2 (speed signal) (when the substraction of voltages Ul and U2 (speed signal) changes from high voltage to low voltage values or vice versa), according to the invention, the addition of the voltages Ul and U2 is sampled and held 11 by a sample and hold element 25. This sample and hold element 25 has hysteresis levels 12, 13.

Fig. 4 shows, besides the already discussed elements, an amplifier 22 and a comparator 23 as well as a state machine 24 in the top path. There is also an element 26, which subtracts the addition of the two output voltages Ul and U2 and the result of the sample and hold element 25. This leads to a result, which is an input data for a comparator 27 with a hysteresis. With the help of the elements 21, 25, 26 and 27 it can be detected, whether the voltage of the addition of Ul and U2 is crossing the hysteresis levels 12, 13 and in which direction. According to the invention this result can be used for detection of the movement direction. Around the sample and hold value of the direction signal hysteresis levels 12, 13 are applied. Depending whether the signal crosses the upper or the lower hysteresis level 12, 13 after the transition of the substraction of voltages Ul and U2 (speed signal) 8, forward or backward motion of the target wheel is detected. This method allows direction detection without the complexity of the compensation of the direction channel described before. An advantage of this method is the possibility to detect the movement direction for rotations of even less than one gear, while the state-of-the-art of said compensation method usually needs more than one full signal period in order to detect maximum and minimum signal levels. The described method allows an extremely fast determination of the target wheel direction, which can be advantageously used for vibration detection and suppression. An easy

method possible with the described algorithm is to wait for at least two gears passing by the sensor in the same direction. In that case the target wheel movement is considered to be a valid rotational movement. In case of an alternating direction signal, the target wheel movement is considered to be a vibration and can be suppressed by the sensor. Applications of the invention are rotational speed sensors for ABS, transmission and crank shaft.

Summarizing the above-mentioned explanations the Fig. 4 shows a block diagram of the proposed setup. The substraction of voltages Ul and U2 (speed signal) from the magnetoresistive bridge will be amplified and converted into a pulse train. The bottom path is used to sum up the two half-bridge signals. A sample and hold element 25 is controlled by the internal state machine 24 and used to sample the addition of voltages Ul and U2 (sum signal) as the transitions of the substraction of voltages Ul and U2 (speed signal). A comparator 27 determines, whether the addition of voltages Ul and U2 (sum signal) is within the hysteresis window 12, 13 around the value held by the sample and hold element 25 or outside of this hysteresis window 12, 13. This information is used by the state machine 24 in order to detect a possible vibration of the target wheel. If no vibration is detected, the sign of the comparator output gives the direction of the target wheel, which is usually a gear wheel.

Fig. 5 illustrates a flowchart, which depicts the detection of the movement direction. This flowchart is the schematic illustration of the inventive proceeding, which is also depicted in Figs 3 and 4. The flowchart has the starting symbol 29, which leads unconditionally to rhombus 30. Because of this rhombus 30 the sample and hold element 25 is switched into the tracking mode. With the help of the element 31, it is detected whether the substraction of voltages Ul and U2 (speed signal) 8 has a negative edge 9. If there is no negative edge 9, it will be further and further tested whether there is one. Therefore, the proceeding according Fig. 5 stops until there is a negative edge 9. If there is a negative edge 9, it will be further proceeded with the rhombus 32. According to the rhombus 32 the sample and hold element 25 is switched into the hold-mode. Therefore, the voltage at this time is kept by the sample and hold

element 25. Then it is checked, whether the comparator hysteresis levels 12, 13 are crossed by the addition of the voltages Ul and U2 10. As long as the comparator hysteresis levels 12, 13 are not crossed, the proceeding can not leave this rhombus 33. In the case the lower level hysteresis 13 is crossed the result thereof is, that a forward movement is detected. If the upper hysteresis level 12 is crossed the result thereof is that a backward movement is detected. After the detection of the direction of the movement is terminated, the proceeding starts again with the rhombus sample and hold element 30, which is switched again in the tracking mode.

Fig. 6 shows a flow chart, which depicts the proceeding of detecting vibration. The proceeding starts with the rhombus 36, which can be also a power-up. Next, there is a request 37, whether there is a edge of the substraction of voltages Ul and U2 (speed signal). The proceeding is stopped at this stage as long as there is none. If there is a edge of the substraction of voltages Ul and U2 (speed signal) arrived, it is detected (for example, with the help of a proceeding according the flowchart as described in Fig. 5) whether there is a forward or backward movement 38. Then in a second stage once again the proceeding waits for a edge of the substraction of voltages Ul and U2 (speed signal) 39, 41. Also again the movement direction is detected 40, 42. In the case that twice a forward movement or twice a backward movement is detected the next step will be rhombus 44 and a valid movement is diagnosed. If there is detected first a forward movement and afterwards a backward movement, the result thereof must be vibration, because the movement is not constant in the same direction. The procedure leads then to the rhombus 43. If there is detected first a backward movement and afterwards in a next step a forward movement the result thereof has to be vibration too. In this case the proceeding arrives at rhombus 45. After a valid movement is diagnosed output pulses will be sent, 46. After vibration is detected, 43 and 45, the proceeding continues with the rhombus 36 and the proceeding starts once again.

Fig. 7 shows a flowchart, which depicts an exemplary embodiment of the invention. According to this embodiment the proceeding is triggered by the edges of the substraction of voltages Ul and U2 (speed signal) 8. As soon as there is a negative edge

of the substraction of voltages Ul and U2 (speed signal) 9 (negative speed edge 48) the addition of voltages Ul and U2 (sum signal) will be sampled 49. Then the proceeding waits until the addition of voltages Ul and U2 (sum signal) is outside of the hysteresis window 12, 13 and there is a positive edge of the substraction of voltages Ul and U2 (speed signal 8) (positive speed edge 51). After both conditions are fulfilled it is detected whether the addition of voltages Ul and U2 (sum signal) 10 is greater than the sampled addition of voltages Ul and U2 (sampled signal) 11. In this case a forward movement is detected, 53. In the other case a backward movement is detected, 54. The proceeding continues with sampling the addition of voltages Ul and U2 (sample sum signal), 55. Therefore, the addition of voltages Ul and U2 (sum signal) is sampled concurrently with a positive edge of the substraction of voltages Ul and U2 (speed signal 8). Then the proceeding waits until the addition of voltages Ul and U2 (sum signal) is outside of the hysteresis window 12, 13 and there is a negative edge of the substraction of voltages Ul and U2 (speed signal) 9. After both conditions occurred there is a test whether the sampled addition of voltages Ul and U2 (sampled signal) 11 is greater than the addition of voltages Ul and U2 (sum signal). In this case a forward movement is detected 59. In the other case a backward movement is detected 60. The proceeding continues with the rhombus 49.

The algorithm shown in Fig. 7 not only allows for a direction detection by comparing maximum and minimum of the sampled addition of voltages Ul and U2 (sampled signal) but also implements indirectly a vibration suppression. This is achieved by implementing a hysteresis window 12, 13 around the sampled value of the addition of voltages Ul and U2 (sampled signal) 11. Only if the addition of voltages Ul and U2 (sum signal) is outside of the hysteresis window 12, 13 a transition of the signal is considered to be valid.

According to an exemplary embodiment it is described a sensor and a method for detecting a moving direction as well as vibration of for example a target wheel. It is disclosed, that the substraction of voltages Ul and U2 (speed signal) from the magnetoresistive bridge will be amplified and converted into a pulse train. A

bottom path is used to sum up the two half-bridge signals. A sample and hold element 25 is controlled by the internal state machine 24 and used to sample the addition of voltages Ul and U2 (sampled signal) as the transitions of the substraction of voltages Ul and U2 (speed signal). A comparator 27 determines, whether the addition of voltages Ul and U2 (sum signal) is within the hysteresis window 12, 13 around the value held by the sample and hold element 25 or outside of this hysteresis window 12, 13. This information is used by the state machine 24 in order to detect a possible vibration of the target wheel. If no vibration is detected, the sign of the comparator 27 output gives the direction of the target wheel.

The target wheel typically is a gear wheel, especially a passive wheel. The target wheel can also be an active magnetized encoder.

List of reference signs:

1 graph Ul -U2

2 line between graph 1 and 3

3 graph U1+U2

4 graph Ul -U2

5 graph U1+U2

6 line between graph 4 and 5

7 graph Ul -U2

8 substraction of voltages Ul and U2 (speed signal)

9 negative edge of the substraction of voltages Ul and U2 (speed signal)

10 graph U1+U2

11 sampled addition of voltages Ul and U2

12 upper hysteresis level

13 lower hysteresis level

14 voltage divider

15 voltage divider

16 element of voltage divider 14

17 element of voltage divider 14

18 element of voltage divider 15

19 element of voltage divider 15

20 sub str actor

21 adder

22 amplifier

23 comparator

24 state machine

25 sample and hold device

26 sub str actor

27 comparator

28 current source

29 start - rhombus

30 SH-element - rhombus

31 Request negative edge of the substraction of voltages Ul and U2 (speed signal) - rhombus

32 SH-element - rhombus 33 Request comparator hysteresis levels crossed - rhombus

34 Forward movement detected - rhombus

35 Backward movement detected - rhombus

36 Start - rhombus

37 Request edge of the substraction of voltages Ul and U2 (speed signal) - rhombus

38 Request movement direction detected - rhombus

39 Request edge of substraction of voltages Ul and U2 (speed signal) - rhombus

40 Request movement direction detected - rhombus 41 Request edge of the substraction of voltages Ul and U2 (speed signal) - rhombus

42 Request movement direction detected - rhombus

43 Vibration detected - rhombus

44 Valid movement - rhombus 45 Vibration detected - rhombus

46 Send output pulses - rhombus

47 Start - rhombus

48 Request negative edge of the substraction of voltages Ul and U2 (speed signal) - rhombus 49 Sample addition of voltages Ul and U2 (sample sum signal) - rhombus

50 Request addition of voltages Ul and U2 (sum signal) outside of hysteresis window - rhombus

51 Request positive edge of the substraction of voltages Ul and U2 (speed signal) - rhombus 52 Request addition of voltages Ul and U2 (sum signal) greater than sampled addition of voltages Ul and U2 (sampled signal) - rhombus

Forward movement detected - rhombus Backward movement detected - rhombus Sample addition of voltages Ul and U2 (sample sum signal) - rhombus Request addition of voltages Ul and U2 (sum signal) outside of hysteresis window - rhombus Request negative edge of the substraction of voltages Ul and U2 (speed signal) - rhombus Request sampled addition of voltages Ul and U2 (sampled signal) greater than addition of voltages Ul and U2 (sum signal) - rhombus Forward movement detected - rhombus Backward movement detected - rhombus