Motion measuring device and method for measuring motion of wheel

Abstract

A motion measuring apparatus and a method of measuring motion of a wheel are disclosed. A method of measuring motion of a wheel includes providing a first acceleration sensor (108) and a second acceleration sensor (110) configured to measure accelerations about a first measurement axis and a second measurement axis. The second measurement axis is substantially orthogonal to the first measurement axis. A first acceleration with respect to the first measurement axis and the second measurement axis is measured (204), and then a predetermined period of time is waited (220) before a second acceleration with respect to the first measurement axis and the second measurement axis is made. An estimate of the change in acceleration is then calculated (206-210) by combining the measured first and second accelerations in a formulated manner.

Description

Technical Field

[0001] The present invention relates to a motion measuring device of the type that is, for example, mounted on a wheel of a vehicle for measuring the motion of the wheel. The present invention also relates to a method of measuring the motion of a wheel, which method is of the type that measures, for example, the wheel acceleration. Background Art

[0002] One aspect of automotive design is the ability to detect the motion of a vehicle. Detection of the motion of a vehicle (especially at relatively low speeds, such as below 15 kph or even from a stationary state) is desirable in order to know when to take certain courses of action related to the operation of the vehicle, such as measuring tire pressure before the vehicle leaves its starting position, so as to avoid missing an opportunity to correct any maintenance issues.

[0003] It is known to provide a centripetal acceleration sensor to monitor the centripetal acceleration of one or more wheels of a vehicle. However, the performance of such centripetal acceleration sensors is sub-optimal because at low vehicle speeds, the signal-to-noise ratio of the centripetal acceleration detection signal generated by a single (per wheel) centripetal acceleration sensor is poor. Thus, such motion detection is only useful at higher vehicle speeds (such as above 25 kph).

[0004] This is not beneficial because at lower vehicle speeds, such as at 15 kph or below 15 kph, the movement of the vehicle cannot be reliably detected. As mentioned above, it is sometimes desirable to detect the motion of a vehicle at lower speeds because once the vehicle starts moving, certain operations related to the vehicle may be necessary or desirable.

[0005] Another known technique involves monitoring the acceleration on the centripetal axis of a centripetal acceleration sensor in order to detect a phase shift relative to the earth's gravity over different time periods. However, this technique is inefficient for some applications because the time taken to measure the acceleration is too long, such as being unable to perform the measurement within one rotation of a wheel of a vehicle. In addition, the technique is relatively power-consuming, which is an important consideration especially for so-called electric vehicles (EVs).

[0006] European Patent No. 4039509 discloses performing acceleration measurements on the x-axis and z-axis simultaneously at a given moment and comparing the acceleration measurements with corresponding thresholds to determine the state of the vehicle. However, as indicated above, such measurement techniques exhibit a poor SNR at lower vehicle speeds and also inefficiently consume power.

[0007] U.S. Patent No. 6,259,999 relates to acceleration measurements on three axes and combines the measurements at a given moment. However, the disclosed technique inefficiently consumes power and exhibits a poor SNR at lower vehicle speeds.

[0008] U.S. Patent No. 11,441,924 discloses calculating filtered acceleration values and rotational speed values from a single acceleration sensor. The technique calculates the respective sums of the acceleration values and the speed values and compares them with thresholds, respectively. Also, the technique has poor SNR performance at lower vehicle speeds because when the centripetal acceleration is on the order of the gravitational acceleration (which is the case at lower vehicle speeds), detecting motion by sensing motion using a uniaxial acceleration sensor is unreliable due to the contributions of both the centripetal acceleration and the gravitational acceleration to the total acceleration seen by the uniaxial acceleration sensor. SUMMARY OF THE INVENTION

[0009] According to a first aspect of the present invention, there is provided a method of measuring the motion of a wheel, the method comprising: providing a first acceleration sensor and a second acceleration sensor, the first acceleration sensor and the second acceleration sensor being configured to measure accelerations with respect to a first measurement axis and a second measurement axis, the second measurement axis being tangential to the wheel and substantially orthogonal to the first measurement axis with respect to the radial direction of the wheel; measuring a first acceleration with respect to the first measurement axis and the second measurement axis; waiting for a predetermined period of time; measuring a second acceleration with respect to the first measurement axis and the second measurement axis; and calculating an estimate of the change in acceleration by combining the measured first acceleration and the second acceleration in a formulated manner.

[0010] The method may further comprise: comparing the estimate of the change in acceleration with a predetermined threshold to detect the motion of the wheel.

[0011] The first acceleration sensor and the second acceleration sensor may be operatively coupled to an acceleration measurement circuit having a power saving mode; the method may further comprise: placing the acceleration measurement circuit in the power saving mode during the predetermined period of time.

[0012] The method may further comprise: waking up the acceleration measurement circuit from the power saving mode at the end of the predetermined period of time to perform the second acceleration measurement.

[0013] The formulated combination of the measured first acceleration and the second acceleration may comprise: calculating a first absolute value of a first mathematical difference of the acceleration measured with respect to the first measurement axis, and a second absolute value of a second mathematical difference of the acceleration measured with respect to the second measurement axis.

[0014] The formulated combination of the first acceleration and the second acceleration may further comprise: selecting a maximum value from the first absolute value and the second absolute value.

[0015] The formulated combination of the first acceleration and the second acceleration may be: MAX(|a x [t1]-a x[t = 0], a z [t = 1] - a z [t = 0)), where a x [t = 0] and a x [t = 1] can be the acceleration measurements of the first acceleration sensor at the corresponding time indicators t = 0 and t = 1 separated by a predetermined time period, and a z [t = 0] and a z [t = 1] can be the acceleration measurements of the second acceleration sensor at the corresponding time indicators t = 0 and t = 1.

[0016] The formulated combination of the first acceleration and the second acceleration can include: summing the first absolute value and the second absolute value.

[0017] The formulated combination of the first acceleration and the second acceleration can be: ∑(|a x [t = 1] - a x [t = 0]|, |a z [t = 1] - a z [t = 0]|), where a x [t = 0] and a x [t = 1] can be the acceleration measurements of the first acceleration sensor at the corresponding time indicators t = 0 and t = 1 separated by a predetermined time period, and a z [t = 0] and a z [t = 1] can be the acceleration measurements of the second acceleration sensor at the corresponding time indicators t = 0 and t = 1.

[0018] The method may further include: using a comparison of an estimate of the change in acceleration with a predetermined threshold to determine that the wheel is stationary; waiting for a predetermined time period in response to the wheel being determined to be stationary; measuring a third acceleration with respect to a first measurement axis and a second measurement axis; and calculating an estimate of the change in another pair of accelerations by combining the measured second acceleration and the third acceleration in a formulated manner.

[0019] The method may further include: comparing the estimate of the change in another pair of accelerations with a predetermined threshold to detect the movement of the wheel.

[0020] The method may further include: calculating the predetermined threshold using at least one of the following: the radius of the wheel, the placement positions of the first acceleration sensor and the second acceleration sensor on the wheel, the required detection time, and / or the power consumption requirement.

[0021] The placement position can be on the tire of the wheel or on the rim of the wheel.

[0022] The method may further include: generating a trigger signal in response to the detection of the movement of the wheel.

[0023] The pressure of a tire of a wheel can be measured in response to a trigger signal. The pressure of the tire can be transmitted to and analyzed by a control unit. The control unit can be configured to generate a driver warning alert in response to the pressure of the tire being lower than a predetermined value.

[0024] According to a second aspect of the present invention, there is provided a motion measurement device for a wheel, the device comprising: an acceleration sensor device including a first acceleration sensor, a second acceleration sensor, and an acceleration measurement circuitry operatively coupled to the first acceleration sensor and the second acceleration sensor, the first acceleration sensor and the second acceleration sensor being configured to measure accelerations with respect to a first measurement axis and a second measurement axis, wherein the second measurement axis is tangential to the wheel and is substantially orthogonal to the first measurement axis with respect to the radial direction of the wheel; wherein, the acceleration measurement circuitry is configured to measure a first acceleration with respect to the first measurement axis and the second measurement axis in use; the acceleration measurement circuitry is configured to wait for a predetermined period of time; the acceleration measurement circuitry is configured to measure a second acceleration with respect to the first measurement axis and the second measurement axis; and the acceleration measurement circuitry is configured to calculate an estimate of the change in acceleration by combining the measured first acceleration and the second acceleration in a formulated manner.

[0025] Thus, it is possible to provide such a method and device: to measure the movement of a wheel at speeds below 15 kph and even shortly after moving from a stationary state (e.g., within one rotation of the wheel, e.g., as part of the rotation of the wheel). Attributed to the use of an orthogonal acceleration sensor that can detect changes in gravitational acceleration on orthogonal axes, the method and device provide improved detection sensitivity. Compared with other measurement devices and techniques, the acceleration measurement values have a superior signal-to-noise ratio and consume power more efficiently than other measurement devices and techniques. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] With reference to the accompanying drawings, at least one embodiment of the present invention will now be described, by way of example only, in which:

[0027] Figure 1 is a schematic side view of a wheel carrying a motion measurement device in an embodiment of the present invention;

[0028] Figure 2 is Figure 1 a schematic cross-sectional view of the wheel along line A-A;

[0029] Figure 3 is that which constitutes an embodiment of the present invention Figure 1 and Figure 2Schematic diagram of the motion measurement device;

[0030] Figure 4 is another embodiment of the present invention Figure 3 Schematic diagram of the acceleration measurement circuit system of the motion measurement device; and

[0031] Figure 5 is a further embodiment of the present invention Figure 1 、 Figure 2 、 Figure 3 and Figure 4 Flowchart of the method for measuring the motion of the wheel in the embodiment of Detailed implementation mode

[0032] Throughout the following description, the same reference numerals will be used to identify the same parts.

[0033] Referring to Figure 1 and Figure 2 , a wheel 100 of a vehicle (not shown) includes a rim 102 and a tire 104 mounted on the rim 102. The tire 104 is formed of any suitable rubber polymer, the details of which are not important for understanding the embodiments set forth herein and will therefore not be described in further detail.

[0034] In this example, a motion measurement device 106 (such as a tire pressure measurement sensor (TPMS)) is disposed within the tire 104, for example adhered to the inner surface of the tire 104 using any suitable adhesive, so as to measure both the centripetal acceleration and the tangential acceleration of the wheel 100. In other examples, the acceleration measurement device 106 may be located in or on other components of the wheel 100, such as on the inner side of the rim 102, for example attached to a valve (not shown) of the tire 104. Although the motion measurement device 106 is described herein as part of a TPMS, those skilled in the art will appreciate that the motion measurement system 106 may be an independent sensor not forming part of a measurement system.

[0035] Turning to Figure 3 , in this example, the motion measurement device 106 is a module including a first acceleration sensor 108 and a second acceleration sensor 110, the first acceleration sensor 108 and the second acceleration sensor 110 being arranged substantially orthogonally to each other so as to measure orthogonal accelerations, such as tangential acceleration and centripetal acceleration. In this example, these axes are the x-axis and the z-axis respectively, and correspond to the direction tangent to the circumference of the wheel and the radial direction with respect to the wheel.

[0036] The first acceleration sensor 108 and the second acceleration sensor 110 are operatively coupled to an acceleration measurement circuit system 112, which is operatively coupled to a power supply 114 (such as a battery) and a communication module 116 (such as a radio frequency (RF) communication module), such as a communication module compliant with Bluetooth TM standards. When part of a TPMS, the communication module can communicate with a vehicle control unit (VCU).

[0037] Reference Figure 4 , the acceleration measurement circuit system 112 includes an x-axis acceleration sensor port 118 and a z-axis acceleration sensor port 120 that are respectively operatively coupled to the first acceleration sensor 108 and the second acceleration sensor 110. The x-axis acceleration sensor port 118 and the z-axis acceleration sensor port 120 are also respectively operatively coupled to an x-axis signal reader circuit 122 and a z-axis signal reader circuit 124. The x-axis signal reader circuit 122 and the z-axis signal reader circuit 124 are also respectively operatively coupled to a controller circuit 126.

[0038] The output of the x-axis signal reader circuit 122 is operatively coupled to a first input of a difference calculator circuit 128, and the output of the z-axis signal reader circuit 124 is operatively coupled to a second input of the difference calculator circuit 128. The first input and the second input of the difference calculator circuit 128 are respectively operatively coupled to a first buffer 130 and a second buffer 132. The first buffer 130 and the second buffer 132, and the first input and the second input of the difference calculator circuit 128 are operatively coupled to a subtraction circuit 134, which has a first output and a second output. The role of the first buffer 130 and the second buffer 132 is to store the corresponding conceptual previous measurement variables acc_x0, acc_z0, and their applications will be further explained in detail later in this article.

[0039] The first output and the second output of the subtraction circuit 134 are respectively operatively coupled to inputs of a first absolute value calculation circuit 136 and a second absolute value calculation circuit 138. The outputs of the first absolute value calculation circuit 136 and the second absolute value calculation circuit 138 are operatively coupled to a first input and a second input of a summation circuit 140, and the output of the summation circuit 140 is operatively coupled to a first input of a comparator circuit 142. A second input of the comparator circuit 142 is operatively coupled to the controller circuit 126, and the controller circuit 126 is also operatively coupled to a memory 144 capable of storing a threshold A E , such as a digital memory. The output of the comparator circuit 142 is operatively coupled to an output port 143 of the acceleration measurement circuit system 112, and the output port of the acceleration measurement circuit system 112 is operatively coupled to the communication module 116, as described above with respect toFigure 3 as described above

[0040] The acceleration measurement circuit system 112 described above is purely exemplary and can be implemented in a variety of different ways depending on implementation preferences. In this example, the blocks and described functions refer to implementation as physical electronic circuits in the analog domain, but hybrid implementations can also be envisioned. The x-axis signal reader circuit 122 and the z-axis signal reader circuit 124 provide analog-to-digital conversion of the analog measurement values obtained from the first acceleration sensor 108 and the second acceleration sensor 110. In this regard, it should be understood that the functions of the blocks described herein are not limited to a specific single-function circuit, such as a comparator circuit, and other analog or digital implementations are envisioned.

[0041] In operation ( Figure 5 ), at startup, the controller circuit 126 of the acceleration measurement circuit system 112 is initialized (step 200). In this regard, the controller circuit 126 instructs the x-axis signal reader circuit 122 and the z-axis signal reader circuit 124 to measure (step 202) the x-acceleration value with respect to the x-axis and the z-acceleration value with respect to the z-axis, which are respectively stored in the first buffer 130 and the second buffer 132. The x-acceleration value acc_x t and the z-acceleration value acc_z t are with respect to the current time period t, where t = 0. The measurement process performed by the x-axis signal reader circuit 122 and the z-axis signal reader circuit 124 may include: respectively querying the first acceleration sensor 108 and the second acceleration sensor 110, and obtaining a single reading of the acceleration with respect to the x-axis and the z-axis. Or in other embodiments, the measurement process may include signal processing techniques, for example, each of the x-axis signal reader circuit 122 and the z-axis signal reader circuit 124 may obtain multiple readings of the acceleration with respect to the x-axis and the z-axis, and filter each of the multiple acceleration readings with respect to the x-axis and the multiple accelerations with respect to the z-axis, such as averaging, so as to obtain the averaged acceleration value with respect to the x-axis and the averaged acceleration value with respect to the z-axis. The averaged acceleration values can be used as the x-axis acceleration measurement and the z-axis acceleration measurement respectively.

[0042] Thereafter, the motion measurement device 106 enters (step 204) a power-saving mode (such as a sleep mode) for a predetermined time period Δt, during which the motion measurement device 106 uses the minimum power from the power supply 114. At the end of the predetermined time period Δt, the acceleration measurement circuit system 112 is woken up from the power-saving mode, for example, by the controller circuit system 126, and subsequent measurements acc_x t and acc_z t are performed (step 206) with respect to the current but now subsequent time period, where t = 1.

[0043] Under the control of the controller circuit 126, the difference calculator circuit 128 receives the x-axis acceleration measurement and the z-axis acceleration measurement, and the subtraction circuit 134 calculates (step 208) the difference with respect to the x-axis acceleration and the z-axis acceleration. Thus, with respect to the x-axis, the difference calculator circuit 128 calculates the x-axis difference between the current measurement of the x-axis acceleration (at time indicator t = 1) and the previous measurement of the x-axis acceleration immediately preceding the current measurement of the x-axis acceleration (this previous measurement is the measurement at time indicator t = 0 stored by the first buffer 130). This can be represented algebraically as: a x [t = 1] - a x [t = 0] (1)

[0044] where a x [t = 1] is the current measurement of the x-axis acceleration, and a x [t = 0] is the previous measurement of the x-axis acceleration. Similarly, with respect to the z-axis, the difference calculator circuit 128 calculates the z-axis difference between the current measurement of the z-axis acceleration (at time indicator t = 1) and the previous measurement of the z-axis acceleration immediately preceding the current measurement of the z-axis acceleration (this previous measurement is the measurement at time indicator t = 0 stored by the second buffer 132). This can be represented algebraically as: a z [t = 1] - a z [t = 0] (2)

[0045] where a z [t = 1] is the current measurement of the z-axis acceleration, and a z [t = 0] is the previous measurement of the z-axis acceleration.

[0046] The controller circuit 126 controls the timing of the processing, instructs the difference calculation circuit 128 to output the x-axis difference to the first absolute value calculation circuit 136, and output the z-axis difference to the second absolute value calculation circuit 138. Then, the first absolute value calculation circuit 136 and the second absolute value calculation circuit 138 respectively calculate (step 210) the absolute values of the x-axis difference and the z-axis difference. Then the absolute values of the x-axis difference and the z-axis difference are output to the summing circuit 140, where the summing circuit 140 sums the two provided absolute values (step 212), which can be represented algebraically as: Σ(|a X [t = 1] - a X [t = 0]|, |a Z [t = 1] - a Z [t = 0]|) (3)

[0047] where |a x [t = 1] - a x[t = 0]| is the absolute value of the x-axis difference, and |a z (t = 1] - a z [t = 0]| is the absolute value of the z-axis difference. This sum is an estimate of the change in the measured acceleration of the wheel.

[0048] Although the absolute values calculated in this example are summed, other mathematical functions can also be used, such as taking the maximum of the two absolute values calculated by the first absolute value calculation circuit 136 and the second absolute value calculation circuit 138. This can be algebraically expressed as: MAX(|a x [t = 1] - a x [t = 0]|, |a z [t = 1] - a z [t = 0]|) (4)

[0049] where |a x [t = 1] - a x [t = 0]| is the absolute value of the x-axis difference, and |a z [t = 1] - a z [t = 0]| is the absolute value of the z-axis difference. In this example, the selected maximum value is an estimate of the change in the measured acceleration of the wheel.

[0050] However, in this example, the summation function is performed, and the resulting sum of the two absolute values represents the measurement of the motion of the wheel (and thus the vehicle to which it is attached), and the resulting sum is compared with a predetermined threshold A E for comparison (step 214) to detect the motion (e.g., of the wheel). Threshold A E is retrieved by the controller circuit 126 from the memory 144 and provided to the comparator circuit 142 for comparison with the sum of the two absolute values as described above (step 214). Any suitable formula can be used to calculate the predetermined threshold A for the estimated change in acceleration E , and suitable formulas can include variables such as the radius of the wheel, the placement positions of the first and second acceleration sensors on the wheel, the required detection time, and / or power consumption requirements.

[0051] The comparison process performed by the comparator circuit 142 produces a logic 1 or 0 output, depending on whether the threshold A E has been exceeded by the calculated sum of the two absolute values (step 216). In determining that the threshold A has not been exceeded E(i.e., no motion has been detected), the subtraction circuit 134 overwrites (step 218) the data in the first buffer 130 and the second buffer 132 regarding the time indicator t = 0, and replaces the data in the first buffer 130 and the second buffer 132 with the current measurements of the x-axis acceleration and the z-axis acceleration for the time indicator t = 1, respectively. Then, the controller circuit 126 again places (step 204) the motion measurement device 106 including the acceleration measurement circuitry 112 into a power-saving or low-power mode for a predetermined time period Δt. At the end of the predetermined time period Δt, the acceleration measurement circuitry 112 is awakened, for example, by the controller circuitry 126 from the power-saving mode, and subsequent measurements are made again (step 206) regarding the time indicator variable t having a unit value, and the above process (steps 208 to 216) is repeated regarding: the newly acquired measurement of the x-axis acceleration (regarding the current measurement point t = 1), the previously measured x-axis acceleration newly stored in the first buffer 130 (regarding the previous measurement point t = 0), the newly acquired measurement of the z-axis acceleration (regarding the measurement point t = 1), and the previously measured z-axis acceleration newly stored in the second buffer 132 (regarding the previous measurement point t = 1).

[0052] However, in the case where it is determined that the threshold A E has been exceeded (i.e., motion has been detected), in this example, the output of the comparator circuit 142 is used as a trigger signal, which is transmitted via the output port 143 of the acceleration measurement circuitry 112 to the communication module 116. In response to the trigger signal, other actions can be performed (step 216), and in fact, if the motion measurement device 106 is part of another device having other measurement capabilities (such as tire pressure measurement capabilities), the trigger signal can be used to initiate a tire pressure measurement. However, it should be appreciated that other operations can be performed in response to the trigger signal, such as waking up other integrated circuits and / or sensing other physical parameters, such as temperature. In the case where a TPMS is employed, the communication module 116 can be used to transmit the performed tire pressure measurement to the above-mentioned VCU. Then, the VCU can be configured to provide a warning message and / or an audible alarm to the driver of the vehicle in the case of too low tire pressure.

[0053] Although in the above example, the measurements of the x-axis acceleration and the z-axis acceleration are processed by the acceleration measurement circuitry 112 to implement the formula of equation (3), it should be appreciated that the acceleration measurement circuitry 112 can be configured to implement the processing according to other formulated combinations of the measurements of the x-axis and z-axis accelerations (e.g., according to equation (4) or any other suitable formulated combination of acceleration measurements).

[0054] Although a predetermined time period is not waited for before estimating a change in acceleration during an initial iteration of the above method, a predetermined time period is waited for in subsequent iterations to provide improved power consumption performance. Thus, it is not necessary to wait for a predetermined time period in the first iteration because, in one of a large number of cases, when the vehicle (e.g., an electric vehicle or EV) is powered on, a predetermined time period is waited for and the motion measurement device 106 enters a power saving mode throughout the operation of the motion measurement device 106.

[0055] For additional information, those skilled in the art will appreciate that the acceleration measurement circuitry 112 described above is used to read the first acceleration sensor 108 and the second acceleration sensor 110 and perform calculations on signals that are read and represent measurements of acceleration. The acceleration measurement circuitry 112 can be formed as a dedicated circuit or a programmable circuit, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). In this regard, the calculations can be performed by a local low-power processor in the digital domain, such as a processor that employs a reduced instruction set computer (RISC) architecture (such as an advanced RISC machine (ARM) or a RISC-V architecture). The logic for reproducing the described functionality can be a channel gate that is combined in any suitable manner for processing the received signals and generating an estimate of the acceleration of the wheel.

Claims

1. A method for measuring the movement of a wheel, the method comprising: Providing a first acceleration sensor and a second acceleration sensor, the first acceleration sensor and the second acceleration sensor being configured to measure accelerations with respect to a first measurement axis and a second measurement axis, the second measurement axis being tangential to the wheel and substantially orthogonal to the first measurement axis with respect to the radial direction of the wheel; Measuring a first acceleration with respect to the first measurement axis and the second measurement axis; Waiting for a predetermined period of time; Measuring a second acceleration with respect to the first measurement axis and the second measurement axis; And Calculating an estimate of the change in acceleration by combining the measured first acceleration and the second acceleration in a formulated manner.

2. The method according to claim 1, further comprising: Comparing the estimate of the change in acceleration with a predetermined threshold to detect the movement of the wheel.

3. The method according to claim 1 or claim 2, wherein The first acceleration sensor and the second acceleration sensor are operatively coupled to an acceleration measurement circuit having a power saving mode; the method further comprising: Placing the acceleration measurement circuit in the power saving mode during the predetermined period of time.

4. The method according to claim 3, further comprising: Waking up the acceleration measurement circuit from the power saving mode at the end of the predetermined period of time to perform the second acceleration measurement.

5. The method according to claim 1 or claim 2, characterized in that, The formulated combination of the measured first acceleration and the second acceleration includes: Calculating a first absolute value of a first mathematical difference of the acceleration measured with respect to the first measurement axis and a second absolute value of a second mathematical difference of the acceleration measured with respect to the second measurement axis.

6. The method according to claim 5, wherein The formulated combination of the first acceleration and the second acceleration further includes: Selecting the maximum value from the first absolute value and the second absolute value.

7. The method according to claim 6, wherein The formulated combination of the first acceleration and the second acceleration is: MAX(|a x [t = 1] - a x [t = 0]|, |a z [t = 1] - a z [t = 0]|) where a x [t = 0] and a x [t = 1] are acceleration measurements of the first acceleration sensor at respective time indicators t = 0 and t = 1 separated by the predetermined time period, and a z [t = 0] and a z [t = 1] are acceleration measurements of the second acceleration sensor at the respective time indicators t = 0 and t = 1.

8. The method according to claim 5, wherein The formulated combination of the first acceleration and the second acceleration includes: Summing the first absolute value and the second absolute value.

9. The method according to claim 8, wherein The formulated combination of the first acceleration and the second acceleration is: ∑(|a x [t = 1] - a x [t = 0]|, |a z [t = 1] - a z [t = 0]|) where a x [t = 0] and a x [t = 1] are the acceleration measurements of the first acceleration sensor at the respective time indicators t = 0 and t = 1 that are separated by the predetermined time period, and a z [t = 0] and a z [t = 1] are the acceleration measurements of the second acceleration sensor at the respective time indicators t = 0 and t = 1.

10. The method according to claim 2, further comprising: Using the comparison of the estimate of the change in acceleration with the predetermined threshold to determine that the wheel is stationary; Waiting for the predetermined period of time in response to the wheel being determined to be stationary; Measuring a third acceleration with respect to the first measurement axis and the second measurement axis; And Calculating an estimate of another change in acceleration by combining the measured second acceleration and the third acceleration in a formulated manner.

11. The method according to claim 10, further comprising: Comparing the estimate of the another change in acceleration with the predetermined threshold to detect the movement of the wheel.

12. The method according to claim 2, further comprising: The predetermined threshold is calculated using at least one of the following: the radius of the wheel, the placement positions of the first acceleration sensor and the second acceleration sensor on the wheel, the required detection time, and / or the power consumption requirement.

13. The method according to claim 12, characterized in that, The placement position is on the tire of the wheel or on the rim of the wheel.

14. The method according to claim 2, further comprising: generating a trigger signal in response to detection of movement of the wheel.

15. A motion measurement device for a wheel, the device comprising: an acceleration sensor device including a first acceleration sensor, a second acceleration sensor, and acceleration measurement circuitry operatively coupled to the first acceleration sensor and the second acceleration sensor, the first acceleration sensor and the second acceleration sensor being configured to measure accelerations with respect to a first measurement axis and a second measurement axis, wherein the second measurement axis is tangential to the wheel and is substantially orthogonal to the first measurement axis with respect to the radial direction of the wheel; wherein the acceleration measurement circuitry is configured to measure a first acceleration with respect to the first measurement axis and the second measurement axis in use; the acceleration measurement circuitry is configured to wait for a predetermined period of time; the acceleration measurement circuitry is configured to measure a second acceleration with respect to the first measurement axis and the second measurement axis; and the acceleration measurement circuitry is configured to calculate an estimate of the change in acceleration by combining the measured first acceleration and the second acceleration in a formulated manner.

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