Robust ‘hands on steering wheel’ classification based on a relative measurement system

Patent metadata

Field	Value
Publication number	US-12015398-B2
Application number	US-202118038739-A
Country	US
Kind code	B2
Filing date	Nov 24, 2021
Priority date	Nov 25, 2020
Publication date	Jun 18, 2024
Grant date	Jun 18, 2024

Abstract

A method of operating a capacitive sensing device that includes a capacitive sensor having at least one sense electrode, a measurement signal source for providing an alternating electric measurement signal with at least three fixed predefined signal frequencies to the at least one sense electrode, and an impedance measurement circuit for determining an unknown complex impedance of the at least one sense electrode from a response to the provided electric measurement signal. The method includes, for each predefined signal frequency: determining statistical quantities and signal parameters regarding a number of determined momentary values of an unknown complex impedance; eliminating portions up to a predefined hand touch movement lower limit frequency and from a predefined high-frequency limit down to a predefined hand touch movement upper limit frequency; excluding statistical outliers from determined momentary values; and using an eliminated frequency portion for calculating a momentary reference value for the unknown complex impedance.

First claim

The invention claimed is:

1. A method of operating a capacitive sensing device that includes:
at least one capacitive sensor having at least one sense electrode,
a measurement signal source configured to provide an alternating electric measurement signal comprising at least three fixed predefined signal frequencies at least to the at least one sense electrode,
an impedance measurement circuit configured to determine an unknown complex impedance of the at least one sense electrode from a response to the provided electric measurement signal,

the method comprising at least the following steps:
operating the measurement signal source to provide an alternating electric measurement signal comprising at least three fixed predefined signal frequencies to the at least one sense electrode,
by the impedance measurement circuit, measuring a response to the alternating electric measurement signal to determine an unknown complex impedance of the at least one sense electrode,

the method further comprising at least the following steps that are to be executed for each of the at least three fixed predefined signal frequencies:
determining a predefined number of momentary values of the unknown complex impedance,
determining statistical quantities and signal parameters regarding the determined momentary values,
eliminating from the determined momentary values a frequency portion up to a predefined hand touch movement lower limit frequency,
eliminating from the determined momentary values a frequency portion from a predefined high-frequency limit down to a predefined hand touch movement upper limit frequency for obtaining remaining determined momentary values,
excluding the respective determined momentary values if at least one determined statistical quantity exceeds a predefined critical threshold value,
using the eliminated frequency portion up to the lower limit frequency of the determined momentary values for calculating a momentary reference value for the unknown complex impedance,

and further comprises the steps of
using the remaining determined momentary values for determining a signal classification by checking a fulfillment of at least one predefined condition that includes the momentary reference value for the unknown complex impedance, and
generating an output signal that is representative of the result of the step of checking the fulfillment of the at least one predefined condition.

2. The method as claimed in claim 1 , wherein the step of eliminating from the determined momentary values the frequency portion from a predefined high-frequency limit down to the predefined hand touch movement upper limit frequency further includes a subsequent step of averaging the magnitudes of the obtained remaining determined momentary values.

3. The method as claimed in claim 1 , wherein the steps of eliminating from the determined momentary values a frequency portion each include a preceding step of calculating a time derivative of magnitudes of consecutively determined momentary values of the unknown complex impedance, and wherein the steps of eliminating are based at least on using the calculated time derivative.

4. The method as claimed in claim 1 , wherein the step of checking a fulfillment of at least one predefined condition includes checking if an absolute difference between the magnitude of the remaining determined momentary values and the magnitude of the momentary reference value for the unknown complex impedance exceeds a predefined threshold value for the magnitude.

5. The method as claimed in claim 1 , wherein the step of checking a fulfillment of at least one predefined condition includes checking if in a predefined period of time a sum of magnitudes of consecutively occurring signal changes of the remaining determined momentary values exceeds a predefined threshold value for the sum of magnitudes of signal changes.

6. The method as claimed in claim 1 , wherein the step of determining a predefined number of momentary values of the unknown complex impedance includes sampling with a sampling period that lies between 0.1 ms and 100 ms.

7. The method as claimed in claim 1 , further comprising a step of immediately adapting the momentary reference value upon a fulfillment of at least one condition including a time derivative of magnitudes of consecutively determined momentary values of the unknown complex impedance.

8. The method as claimed in claim 1 , further comprising a step) of immediately adapting the momentary reference value upon a fulfillment of the condition that the magnitude of the momentary reference value is smaller than the magnitude of the latest precedingly calculated reference value for the unknown complex impedance.

9. The method as claimed in claim 1 , further comprising a step to be executed once in a driving cycle of a vehicle of adapting the momentary reference value upon a fulfillment of the condition that an ambient temperature rise or an ambient humidity rise at the at least one capacitive sensor exceeds a predefined threshold for the ambient temperature rise or the ambient humidity rise, respectively, wherein the amount of adapting is determined from an a priori known temperature-dependence or humidity-dependence, respectively, of a material in the vicinity of the at least one sense electrode of the at least one capacitive sensor.

10. A capacitive sensing device including:
at least one capacitive sensor having at least one sense electrode,
a measurement signal source that is configured for providing an alternating electric measurement signal comprising at least three fixed predefined signal frequencies at least to the at least one sense electrode,
an impedance measurement circuit that is configured for determining an unknown complex impedance of the at least one sense electrode with regard to a reference potential from a response to the provided electric measurement signal, and
an electronic evaluation and control unit that is configured to automatically execute steps of the method as claimed in claim 1 .

11. A vehicle steering wheel with capacitive hands off detection, comprising a capacitive sensing device as claimed in claim 10 .

12. Use of a capacitive sensing device as claimed in claim 10 in a vehicle steering wheel for at least one of capacitive hands off detection and capacitive hand position detection.

13. A software module for controlling an automatic execution of the method as claimed in claim 1 , wherein the method steps comprise a program code of the software module, wherein the program code is implementable in a digital data memory unit of a control unit and is executable by a processor unit of the control unit.

Assignees

• Iee Sa

Inventors

• Faber Thomas
• Althaus Frank
• Meyers Thomas
• Lion Oliver
• Lamesch Laurent
• Pütz Michael
• Koehler Alan

Classifications

• H03K2217/96078

  Sensor being a wire or a strip, e.g. used in automobile door handles or bumpers · CPC title

• H03K2217/960735

  characterised by circuit details · CPC title

• H03K2217/96071

  characterised by the detection principle · CPC title

• B62D1/046

  Adaptations on rotatable parts of the steering wheel for accommodation of switches · CPC title

• H03K2217/960705

  Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe · CPC title