Sensor for sensing accelerations
Sensors ( 1 ) for sensing accelerations are provided with accelerometers ( 11 ) for measuring accelerations, with magnetometers ( 12 ) for measuring magnetic fields, and with processors ( 13 ) for, in response to acceleration measurements and magnetic field measurements, judging the accelerations. The processors ( 13 ) may comprise acceleration units ( 14 ) for comparing acceleration signals with acceleration thresholds, and magnetic field units ( 15 ) for comparing changes of magnetic field signals per time interval with rate thresholds. The processors ( 13 ) may further comprise decision units ( 17 ) for, in response to comparison results from the acceleration units ( 14 ) and the magnetic field units ( 15 ), deciding whether a total acceleration forms part of a tumbling free-fall or a non-tumbling free-fall or not. The processors ( 13 ) may yet further comprise distinguishing units ( 18 ) and control units ( 19 ). Devices ( 2 ) may comprise sensors ( 1 ).
1. A sensor for sensing accelerations, which sensor comprises:
an accelerometer for measuring an acceleration,
a magnetometer for measuring a magnetic field, and
a processor for, in response to at least one acceleration measurement measured by the accelerometer and at least one magnetic field measurement measured by the magnetometer, judging the acceleration,
the processor comprising:
an acceleration unit for comparing the at least one acceleration measurement measured by the accelerometer with at least one acceleration threshold,
a magnetic field unit for comparing at least one change of the at least one magnetic field measurement measured by the magnetometer per time interval with at least one rate threshold, and
a decision unit for, in response to comparison results from the acceleration unit and the magnetic field unit, deciding whether a total acceleration forms part of a tumbling free-fall or a non-tumbling free-fall, wherein the decision unit is configured to decide that the total acceleration forms part of a non-tumbling free-fall if the deviation of the total acceleration from a fixed acceleration value is larger than a first threshold while the rate of change of each of the at least one magnetic field measurement is smaller than the at least one rate threshold and if the time integral of the deviation of the total acceleration is larger than a second threshold.
2. The sensor according to claim 1 , the accelerometer comprising an at least two dimensional accelerometer for measuring the acceleration in at least two dimensions and for generating at least two acceleration signals per acceleration measurement.
3. The sensor according to claim 1 , the magnetometer comprising an at least two dimensional magnetometer for measuring the magnetic field in at least two dimensions and for generating at least two magnetic field signals per magnetic field measurement.
4. The sensor according to claim 1 , the processor further comprising:
a control unit for, in response to at least one comparison result from the acceleration unit and/or the magnetic field unit, controlling a clock signal generator for generating a variable clock signal defining a variable bandwidth rate and/or a variable sampling rate.
5. A device comprising the sensor according to claim 1 , the acceleration being the acceleration of the device.
6. The sensor of claim 1 , wherein the decision unit is configured to decide that the total acceleration forms part of a tumbling free-fall if the at least one acceleration measurement measured by the accelerometer is larger than the at least one acceleration threshold and if the at least one change of the at least one magnetic field measurement measured by the magnetometer per time interval is larger than the at least one rate threshold.
7. A sensor for sensing accelerations, which sensor comprises:
an accelerometer for measuring an acceleration,
a magnetometer for measuring a magnetic field, and
a processor for, in response to at least one acceleration measurement measured by the accelerometer and at least one magnetic field measurement measured by the magnetometer, judging the acceleration,
the processor comprising:
an acceleration unit for comparing the at least one acceleration measurement measured by the accelerometer with at least one acceleration threshold,
a magnetic field unit for comparing at least one change of the at least one magnetic field measurement measured by the magnetometer per time interval with at least one rate threshold,
a distinguishing unit for, in response to comparison results from the acceleration unit and the magnetic field unit, distinguishing a first acceleration in a first direction from a second acceleration in a second direction, and
a decision unit for, in response to comparison results from the acceleration unit and the magnetic field unit, deciding whether a total acceleration of at least one of the first and second accelerations forms part of a tumbling free fall or a non-tumbling free-fall, wherein the decision unit is configured to decide that the total acceleration forms part of a non-tumbling free-fall if the deviation of the total acceleration from a fixed acceleration value is larger than a first threshold while the rate of change of each of the at least one magnetic field measurement is smaller than the at least one rate threshold and if the time integral of the deviation of the total acceleration is larger than a second threshold.
8. The sensor of claim 7 , wherein the decision unit is configured to decide that the total acceleration forms part of a tumbling free-fall if the at least one acceleration measurement measured by the accelerometer is larger than the at least one acceleration threshold and if the at least one change of the at least one magnetic field s measurement measured by the magnetometer per time interval is larger than the at least one rate threshold.
9. A method for sensing accelerations, which method comprises the steps of:
measuring an acceleration using an accelerometer,
measuring a magnetic field using a magnetometer, and
in response to at least one acceleration measurement measured by the accelerometer and at least one magnetic field measurement measured by the magnetometer, judging the acceleration using a processor,
wherein judging the acceleration comprises:
comparing the at least one acceleration measurement measured by the accelerometer with at least one acceleration threshold,
comparing at least one change of the at least one magnetic field measurement measured by the magnetometer per time interval with at least one rate threshold, and
in response to comparison results, deciding whether a total acceleration forms part of a tumbling free-fall or a non-tumbling free-fall, comprising deciding that the total acceleration forms part of a non-tumbling free-fall if the deviation of the total acceleration from a fixed acceleration value is larger than a first threshold while the rate of change of each of the at least one magnetic field measurement is smaller than the at least one rate threshold and if the time integral of the deviation of the total acceleration is larger than a second threshold.
10. A non-transitory computer readable medium containing computer instructions stored therein for causing a computer processor to perform steps of the method according to the claim 9 .
11. The method of claim 9 , wherein deciding whether the total acceleration forms part of a tumbling free-fall or a non-tumbling free-fall comprises deciding that the total acceleration forms part of a tumbling free-fall if the at least one acceleration measurement measured by the accelerometer is larger than the at least one acceleration threshold and if the at least one change of the at least one magnetic field measurement measured by the magnetometer per time interval is larger than the at least one rate threshold.