# US 12,015,398 B2 · Robust ‘hands on steering wheel’ classification based on a relative measurement system

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- Number: US 12,015,398 B2
- Document ID: US12015398B2
- Status: Granted
- Kind: B2
- Application number: 18/038,739
- Filed: 2021-11-24
- Published: 2023-12-14
- Granted: 2024-06-18
- Earliest claimed: 2020-11-25
- Assignees: Iee International Electronics & Engineering S.A.
- Applicants: Iee International Electronics & Engineering S.A.
- Inventors: Thomas Faber; Frank Althaus; Thomas Meyers; Oliver Lion; Laurent Lamesch; Michael Pütz; Alan Koehler
- Web page: https://patentgrep.com/patent/US12015398B2

## CPC

- H03K 17/962: {Capacitive touch switches}
- B62D 1/046: {Adaptations on rotatable parts of the steering wheel for accommodation of switches}
- H03K 2217/960705: Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
- H03K 2217/96071: characterised by the detection principle
- H03K 2217/960735: characterised by circuit details
- H03K 2217/96078: Sensor being a wire or a strip, e.g. used in automobile door handles or bumpers
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- B62D: MOTOR VEHICLES; TRAILERS (steering, or guiding on a desired track, of agricultural machines or implements A01B69/00; wheels, castors, axles, increasing wheel adhesion B60B; vehicle tyres, tyre inflation or tyre changing B60C; connections between vehicles of a train or the like B60D; vehicles for use on rail and road, amphibious or convertible vehicles B60F; suspension arrangements B60G; heating, cooling, ventilating or other air treating devices B60H; windows, windscreens, non-fixed roofs, doors or similar devices, protective coverings for vehicles not in use B60J; propulsion plant arrangements, auxiliary drives, transmissions, controls, instrumentation or dashboards B60K; electric equipment or propulsion of electrically-propelled vehicles B60L; power supply for electrically-propelled vehicles B60M; passenger accommodation not otherwise provided for B60N; adaptations for load transportation or to carry special loads or objects B60P; arrangement of signalling or lighting devices, the mounting or supporting thereof or circuits therefor, for vehicles in general B60Q; vehicles, vehicle fittings or vehicle parts not otherwise provided for B60R; servicing, cleaning, repairing, supporting, lifting, or manoeuvring, not otherwise provided for, B60S; brake arrangements, brake control systems or parts thereof B60T; air-cushion vehicles B60V; motor-cycles, accessories therefor B62J, B62K; testing of vehicles G01M)

## 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.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

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.

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

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.

### Claim 6 (depends on 1)

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.

### Claim 7 (depends on 1)

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.

### Claim 8 (depends on 1)

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.

### Claim 9 (depends on 1)

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.

### Claim 10 (depends on 1)

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.

### Claim 11 (depends on 10)

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

### Claim 12 (depends on 10)

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.

### Claim 13 (depends on 1)

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.